If you want a faster WordPress site, caching belongs at the center of your performance plan. It reduces the work your server has to do and turns slow, dynamic page builds into quick, static responses. On many unoptimized sites, that shift alone can reduce several seconds off page loads when paired with other best practices. The trick isn’t whether to cache but how to pick the right caching approach for your site’s content, traffic, and infrastructure.
This guide walks you through the major caching layers available to WordPress, the trade‑offs of each option, a brief overview of the settings that matter most, and where caching fits alongside other optimization tactics.
What caching actually does
Every time a non‑cached WordPress page is requested, your server:
- Loads WordPress core and active plugins/themes.
- Queries content and options from MySQL.
- Executes PHP to build the page.
- Sends the final HTML (plus CSS/JS/assets) to the browser.
That full process repeats for every request, which is why it’s resource‑intensive. Page caching short‑circuits the heavy lifting by generating a static HTML copy the first time and serving that on subsequent visits. Most modern plugins can also work with a Content Delivery Network (CDN) so your cached pages are available from data centers near your visitors, reducing latency and helping with traffic spikes.
Key habit: When something significant changes (theme switch, plugin activation/deactivation, major design updates), clear your caches so visitors get the current version. Most plugins purge the cached copy when you update a post or page, but not every change triggers an automatic refresh, so “Clear All Cache” should still be part of your normal operations.
Performance goals and how caching helps
Caching supports, but does not replace, core performance work. It’s especially helpful for improving TTFB (Time to First Byte). By cutting origin processing time through caching retrieval, you’re providing a faster first byte and quicker render start.
It also applies to Google’s main Core Web Vitals:
- LCP (Largest Contentful Paint): Faster HTML delivery and CDN‑served assets often reduce LCP.
- INP (Interaction to Next Paint): Primarily affected by JavaScript; deferring non‑critical scripts can help.
- CLS (Cumulative Layout Shift): Caching can improve CLS indirectly; speeding up load times reduces the chance of layout shifts caused by late-loading elements.
Know your caching layers
While you don’t have to use every type, knowing what they do will help you choose wisely.
Page caching (server‑side)
Page caching is the most effective way to speed up a WordPress site by storing a static HTML version of a page. When a visitor requests a page, the server delivers the pre-generated HTML directly, bypassing the resource-intensive PHP processing and database queries of the standard WordPress execution. This results in significantly faster load times, dramatically reduced server load (improving scalability), and better SEO.
While caching can be implemented via WordPress plugins, the most efficient method is Host- or Server-Level Implementation (e.g., via NGINX or Varnish), where the cache is consulted before the request ever reaches the WordPress application for maximum performance.
Browser caching (client‑side)
Browser caching, or client-side caching, is a performance optimization technique where a web server instructs a visitor’s browser (via HTTP headers like Cache-Control and Expires) to save local copies of static assets (CSS, JS, images, etc.) for a specific time. This mechanism eliminates the need for repeat downloads when the visitor revisits the site, resulting in faster page load times for returning users, reduced server load, and an improved overall user experience.
Control is managed server-side through cache headers, with revalidation handled by ETag and Last-Modified. In a WordPress environment, these settings are typically managed using caching plugins, host-level optimizations, or direct configuration file modifications.
CDN/edge caching
A Content Delivery Network (CDN) is a geographically distributed network of edge servers (PoPs) that fundamentally improves website performance and reliability. Its primary functions include:
- Global Content Distribution by caching static and sometimes dynamic assets on edge servers closest to the user.
- Optimizing Performance (TTFB) by reducing latency for global audiences.
- Managing Traffic by acting as a buffer to cushion against sudden spikes and prevent the origin server from being overwhelmed.
- Enhance Security and Reliability through integrated features like WAFs and DDoS mitigation at the network edge.
Database (object) caching
Object caching involves storing the results of complex and frequently repeated database queries in memory. Its core benefit is dramatically reducing the load on the database server and significantly accelerating data retrieval time, which speeds up page rendering.
Object caching is most beneficial for highly dynamic and complex websites like large e-commerce stores (WooCommerce), membership sites, forums, and high-traffic news portals that generate heavy database interactions. Implementation typically uses specialized, persistent, in-memory systems like Redis or Memcached, requiring server-side configuration and integration via a dedicated WordPress plugin.
Opcode caching
Opcode caching is a server-side optimization that dramatically speeds up PHP applications like WordPress. When a PHP script runs, the human-readable code is compiled into lower-level “opcode” or “bytecode.” An opcode cache (most commonly OPcache) stores this compiled bytecode in memory after the first execution. This bypasses the time-consuming compilation step on subsequent requests, leading to a near-instantaneous speedup.
This process operates at a low, system-wide level, making it a foundational performance boost managed by the hosting environment or server administrator, and is not a setting a WordPress user manages via a site-specific plugin.
Start with your site’s constraints
Before choosing a tool, map your site’s behavior:
- Content type: Mostly static pages/posts vs. dynamic features (carts, dashboards, membership portals).
- Logged‑in traffic: High proportions of authenticated users often need different caching rules.
- Commerce: WooCommerce stores must exclude cart, checkout, and account pages from page caching. Widgets that show cart or order details should be excluded too to avoid inaccurate states.
- Team workflow: How often does content change? Who needs to purge caches, and when?
- Hosting platform: Do you have host‑level caching already? Some providers forbid additional caching plugins to avoid conflicts.
Host‑level/server caching
Many managed WordPress hosts provide caching at the server or reverse‑proxy layer.
Key Advantages:
- Tuned to the stack: Hosts can align cache rules, storage, and purging to their infrastructure for reliable performance.
- Simplicity: No plugin to maintain; fewer knobs to turn.
Trade‑offs:
- Limited customization: Advanced users may feel constrained by “one‑click” setups.
- Troubleshooting friction: You may rely on support to adjust rules or diagnose conflicts.
Lean into these solutions when you prefer simplicity, your host is stable, and your site isn’t a special case that needs granular rules. Keep in mind, your host may prohibit additional caching plugins, so it’s best to follow their guidance to avoid conflicts.
WordPress caching plugins
Caching plugins give you control and often bundle extra performance features (e.g., database cleanup, minification/aggregation, deferring JavaScript, removing unused CSS). Dedicated tools can sometimes outperform “all‑in‑one” features. For example, WP‑Optimize focuses on database cleanup, while Autoptimize is popular for aggregating/minifying CSS/JS/HTML.
If you want granular control (exclusions, separate mobile cache, preload behavior, purging strategy) or your host doesn’t include caching, plugins can provide the tools you need and also make it easy to integrate with a CDN.
Golden rule: Use only one caching plugin at a time. Running multiple caching plugins won’t make your site faster and can lead to issues.
CDN/edge caching
A CDN caches and serves content from locations closer to your visitors. Most caching plugins can connect to a CDN and add proper headers. CDN caching shines when:
- Your audience is globally distributed.
- You experience traffic surges (e.g., promotions, press).
- You want lower TTFB and fewer origin hits.
Pair page caching (at origin) with CDN caching for the best end‑to‑end results.
A repeatable testing workflow
1) Measure a baseline
Use PageSpeed Insights (both mobile and desktop) for field/lab data and Core Web Vitals. Record TTFB, the Core Web Vitals discussed earlier (LCP, INP, CLS), and page size/requests.
2) Enable caching in stages
A phased approach is recommended for enabling caching to ensure stability and minimize risks:
- Prioritize Page Caching: Enable fundamental page caching (HTML output) first for the most immediate and significant performance gain, reducing PHP and database load.
- Implement Browser Cache Headers: Add client-side headers (Expires, Cache-Control) to instruct visitors’ browsers to store static assets (images, CSS, JS) locally, speeding up repeat visits.
- Introduce CDN/Edge Caching: Layer in a Content Delivery Network for global distribution, serving content from the nearest server (PoP) to reduce latency and provide defense against traffic spikes.
- Layer in Performance Optimizations: In the final stage, carefully introduce advanced, higher-risk optimizations like Deferring JavaScript, Minifying Code, and implementing Critical Path CSS (removing unused CSS) after thorough testing.
3) Verify functionality
Verify functionality by testing:
- Authentication States (Login/Logout): Verify users can log in and out correctly, and that personalized, logged-in experiences are never cached for general visitors.
- Interactive Elements and Forms: Test all forms (contact, subscription, comments, etc.) to confirm they submit successfully and correctly bypass the cache to prevent security or submission errors.
- Site Search Functionality: Perform various searches to ensure the results are dynamic, accurate, and not being served from a stale cache.
- E-commerce (If Applicable): Critically test the shopping cart, checkout, and account pages, which must be excluded from caching, by adding, modifying, and ordering items.
- Content Freshness and Cache Purging: Check that new or updated content appears immediately after publishing. If not, verify that the manual cache purge routine reliably clears the cache to display the fresh content.
4) Re‑measure and compare
Expect the biggest gains from page + CDN caching. Use real-user monitoring where available to confirm improvements for your audience and geographies.
When you should or should not cache
Is your host already caching pages?
If so, start there. Ask your host how to purge, how exclusions are handled, and whether a plugin is allowed for fine‑tuning. Avoid overlapping features that duplicate what the host already does.
Do you run WooCommerce or other dynamic features?
Exclude cart, checkout, and account pages and any AJAX/cart fragments or widgets that display per‑user data. Keep page caching for category and product pages where appropriate.
Is a large portion of traffic logged in?
Consider bypassing page cache for logged‑in users or enabling a “separate cache for logged‑in users” if your plugin/stack supports it. Keep object/opcode caching on the server for repetitive operations.
Do you have a global audience?
Add a CDN and enable edge caching of static assets and HTML where safe. Verify your purge workflow clears both origin and CDN caches after updates.
How often do you publish or change design?
Set sensible cache TTLs (time‑to‑live) and use preload/warmup so important pages are cached before the next visit. Build “Clear All Cache” into your release checklist after major updates.
Common issues and FAQ
Q: Why does my page show old content after an update?
Why it happens: A stale cache at the origin server or CDN.
How to fix it: Purge the cached version of the page. If you changed global elements (menus, header, templates), clear all caches (both origin and CDN).
Q: Why do forms or widgets stop working after enabling “defer JS”
Why it happens: A critical script is being delayed.
How to fix it: Exclude the affected script(s) or the specific page(s) from your defer/delay rules.
Q: How come product prices or cart counts are wrong?
Why it happens: Dynamic fragments are being served from page cache.
How to fix it: Exclude WooCommerce cart, checkout, and account pages from page caching, along with cart/AJAX fragments or any relevant cookies used to personalize the view.
Q: Why does my host say “no caching plugins allowed”
Why it happens: Often, this is due to your provider already running server‑level caching and attempting to avoid conflicts.
How to fix it: Use the host’s built‑in caching and follow their purge/exclusion guidance. Disable overlapping plugin features that duplicate the host’s cache.
Q: What should I do if visitors see outdated images or CSS?
Why it happens: Browsers or the CDN are still serving cached assets.
How to fix it: Purge caches at both the origin and CDN. Make sure your deployment checklist includes a full cache clear after theme or asset changes.
Final wrap‑up
Caching is one of the most effective, low‑friction ways to accelerate WordPress. It reduces server work, lowers TTFB, and when paired with solid optimization practices, helps deliver the fast, stable experience search engines and users expect. If you’re weighing host‑level caching against plugins and CDN options, pick the least complex stack that gives you precise control over exclusions and purging. Then test, verify, and iterate. Do that, and you’ll unlock the bulk of the gains available to most WordPress sites and begin shrinking those load times.
Victor Santoyo
Luke Leal
Pilar Garcia
Allison Bondi
Ben Martin![Malware comes in many different varieties. Analyst Krasimir Konov is on this month’s Sucuri Sit-Down to help keep them all straight. From malicious iframes to SEO spam, join host Justin Channell as he racks Krasimir’s brain on all the different types of malware. Also, Krasimir discusses his recent blog post about a malicious cURL downloader, and Justin breaks down the latest website security news, including patched plugins you should update. Podcast Transcript Justin Channell: Hello, and welcome to the Sucuri Sit Down. I'm your host, Justin Channell, and this is a monthly podcast about website security, where we get in-depth with the malware removal experts here at Sucuri. Later in the show, I'll have our analyst Krasimir Konov to chat about some different types of malware, but first, let's take a look at other topics we've published on our blog and Sucuri labs notes this month. First up, we have some new information about credit card skimming with hackers using a hybrid method to steal payment information from eCommerce websites. Our analyst Dennis Sinegubko wrote about this for the Sucuri blog back at the beginning of June. Now, most credit card stealing malware is a client side JavaScript that grabs data and sends it to a third party server. But, that approach has a drawback for bad actors because it's still possible to track the requests and catch them as being suspicious. Now, to get around that, bad actors have started harvesting information server side by modifying core PHP files. In this case, the infection would be undetectable from the outside, but it's still going to be pretty easy to find because you're rarely modifying any of those core files, so any of those changes that are going to come up are going to be suspicious. To get around both of these drawbacks, we're seeing bad actors combine the two. So client side snippets of JavaScript are sending stolen credit card data to server side scripts that they've installed on the same server as the site. Now, this allows bad actors to cover their tracks a little bit because the traffic that's being redirected is going to the same server, and that's less likely to be flagged as suspicious. It's a bit more complicated to pull this off, but our team has been seeing this hybrid approach in the wild, so it's something to be on the lookout for. Now, another month has passed, and we found more cross site scripting attacks targeting WordPress plugins. Most notably, we discovered one that affects users of the YITH WooCommerce Ajax Product Filter plugin. Now, this is a plugin that allows WooCommerce stores to be filtered by product type, and it's pretty popular. It's got about 100,000 users right now, so with it being vulnerable, it's very important that all of them update to the latest version, which is 3.11.1. Some of the other plugins we found cross site scripting vulnerabilities with included Elementor Page Builder, Careerfy, JobSearch, and Newspaper. If you're looking for a full list of vulnerabilities that have been patched this month, John Castro at the Sucuri Labs blog has you covered. Check out our show notes for the link. Also, this month I had a blog go up detailing what's called a jibberish hack. It's basically the same motivation as an SEO spam attack where bad actors use your site's good standing to redirect visitors to their own sites. But in this attack, you'll find a bunch of randomly named folders filled with a ton of HTML files with really nonsensical file names like cheap-cool-hairstyles-photos.html. It's just going to be a mishmash of keywords that clearly you didn't put there. Unfortunately, just deleting all those HTML files and folders is not going to be enough to get rid of that jibberish hack though. You're going to need to fully clean any hacked files and database tables, and then you're going to have to deal with all the damage caused to your site's standing. And just keep in mind, if you find anything about that process too daunting, we're always here to help. Now, for this month's Sit Down, we have Sucuri analyst Krasimir Konov. Earlier in June, he had written a lab's note about a malicious downloader script that used the curl function, and we chatted a bit about it, but more importantly, we went really in-depth on all the different varieties of malware that website owners need to be aware of. But, before I get started with Krasimir, I just wanted to remind you about the Sucuri Sync-Up, our sister podcast. It's a weekly website security news briefing that you can find anywhere you get your podcasts, as well as the video version on our social media feed, and now you can even get it on your Amazon Alexa smart speakers. Just search Amazon skills for Sucuri Sync-Up, add the flash briefing, and get new content delivered every Monday. Now, on with the show. Hi Krasimir, thanks for joining us on the show. I thought we could start off and maybe have you tell us a little bit about yourself and what you do here at Sucuri? Krasimir Konov: Yeah, sure. Well, I joined Sucuri originally in 2014, but I've been in the IT business for about 10 years. Nine of those I did security. And currently at Sucuri I'm one of the malware analysts. I used to work in the front lines, used to clean websites and whatnot, and then I gradually moved up, and now I'm working in the malware research department. And my day to day job is basically analyzing malware, and then once I analyze it and figure out what it is, then I will create a signature for it. And we'll add those signatures to our tools, so we can automate some of the work we do. And I also write some Labs Notes blog posts. Usually, if I find something interesting in malware or some security topic, I'll write about it. Justin Channell: Yeah. And of those topics recently that you wrote about, one was about a malicious curl downloader, and how exactly did that work? Krasimir Konov: Right, yeah. That was an interesting one, but not very unique or anything like that. We see that a lot with curl being used as a downloader. It's a very common malware. So rather than including the actual malware in the file, the attackers would use curl to download the malicious code. In this case, they'll download it from Pastebin, but it could be anything. It could be another website or anything like that, and curl would just make a call to the website, request the code. The website will respond with the code, and then later on, there is some code to either save the output somewhere on the website, or you'll just run it through eval and execute the actual code right away. Justin Channell: Right. And you said that it's commonly found in malware, but let's kind of maybe talk a bit broader about malware in general. What is everything that is classified as malware? Krasimir Konov: Well, in general it will be anything that the owner of the website didn't authorize, anything that was added by a third party. There is a lot of different malware. It could be even something like a defacement that will also be considered malware because it was something the user did not authorize. Even though it might not be doing anything malicious on the website, it's not infecting users, the visit is still something they did not authorize. So defacement would also be considered malware. And even something like ransomware where the website is technically not really damaged, it's all encrypted, but it's not infecting anybody. It's not doing anything malicious, but it's still encrypting the entire website and asking the user or the customer, the owner of the website for a ransom they need to pay in order to get the website back online. Justin Channell: Okay. Let's maybe break it down to each individual type of malware. For example, what would be a way that maybe I-frames could be maliciously used by a hacker? Krasimir Konov: Yeah. An I-frame can be used maliciously when it loads content from another location. You can look at the I-frame as a window that just opens another website. So anything that website has on it, you're pretty much loading it through the I-frame. So if that website is infected and it's serving some kind of malware, by opening an I-frame, you're loading all those elements, everything that was on this website. And sometimes the I-frame can be as small as pixel or something hidden somewhere off the screen, so you wouldn't even know that it was opening it. Justin Channell: And yeah, I feel like we've also seen a lot of them where they're used almost to mimic popups as well. Krasimir Konov: Yeah. I mean the I-frame, it could just load from another website and the other website could do anything. It could be serving just malware and it would try to infect the user that doesn't even know that they're being connected to the other website. It could just have some other JavaScript that's just trying to open up pop ups on the original website through the I-frame. Yeah, it could be a lot of things. Justin Channell: Okay. And also, let's talk a little bit about conditional redirects and how those work. What allows a script to detect which devices are coming in and where they're coming from? Krasimir Konov: Right. Yeah. That's a common one we see a lot. Basically, a conditional redirect would be something, it's a redirect on the website. It's obviously malicious, but there's certain conditions that need to be met before the redirect is actually executed or the redirect happens. For example, let's say if it's on a phishing website or a phishing page that is hidden somewhere on the website. For example, if Google visits it, obviously the attacker doesn't want Google to see the actual phishing page and record it as a phishing page. So they'll look for, for example, the IP address. They would look for the user agent. And a lot of times they can tell that it's a bot. So they'll just return a 404 response, for example, that will be like, "Oh, page not found." So Google would be like, "Oh, it looks like this page doesn't exist." But then if a regular user goes to the same page, then those conditions will be met. The actual website or the script behind the phishing will check and see, and be like, "Oh, this one is running Firefox or Chrome," and be like, okay. And then they'll look at the IP and be like, "Oh, he's in whatever, he's in United States somewhere." And he's like, "Oh, okay. That's good." And then once all of these conditions are met, then the actual script will serve them the actual phishing page. And it'll be like, "Oh, you need to fill out this to recover your account or whatever, or type in your credentials to log in here." Justin Channell: And so this is the type of thing we're really, a website owner is going to run into this more commonly when people are complaining about they're getting served bad content or whatever, and they can't seem to replicate it. It's likely probably these kind of redirects. Is that right? Krasimir Konov: Right, right. It could be something as specific as, for example, a range of IP addresses that correspond to an ISP or maybe let's say a country. It could be like, "Oh, were targeting only customers in the US," so if you're connecting from another country and you go to the same website or the same page, it would just say 404. It will give you a page not found. But then if you actually have an IP address from the United States, you're connecting from the United States, then it will actually show you the phishing page. Justin Channell: Now another type of malware I feel like we see a lot here is SEO spam. We hear people talking about that. What are some of the top SEO spam keywords that you see coming through? Krasimir Konov: Yeah. We get that a lot. We see a lot of spam on websites. A lot of times attackers will use SEO spam to gain ranking for their own website. Or they'll just try to include some kind of SEO spam in links to another website that they're currently running or something. I mean, these things change all the time. So a website might be up for a week and then it'll disappear, and then they'll start another campaign. But yeah, we see that a lot. We see all kinds of keywords they use. Most common ones will be something like Viagra. We'll have like jerseys for sale. A lot of times, they'll use name brands like Nike, Rolex, Prada. We've seen even some essay writing services for some reason. I'm not sure why, but that's common. We see, for example, pharmaceuticals a lot that will use specific medicine names. They'll use all kinds of replicas, like a replica bag of this, replica this, replica that. We'd see prescription, also payday loans. And obviously there's some adult related sites and things like that keywords. Justin Channell: So pretty much anything that people are going to be searching and clicking on are probably going to be targets for SEO spam? Krasimir Konov: Right. I think a lot of it commonly is pharma related because a lot of people are looking to buy medicine online, and a lot of times will require a prescription. So a lot of people are like, "Oh, let me see if I can find this medicine that I can buy it online somewhere." They don't need a prescription. They don't want to pay to visit a doctor and whatnot, and they'll look for it. And yeah. Justin Channell: Now, whenever somebody's website does get hacked with a SEO spam attack, what kind of effect can it have on the website beyond just being defaced? Krasimir Konov: Yeah. You can have a lot of things can happen, negative things. For example, the website can be blacklisted because of the keywords. And that usually represents a big red warning when you go on the website, depending on who blacklisted it. But if it's Google, for example, you'll see a big warning and it'll tell you this website contains malware or there's something wrong with this website. So, pretty much all the traffic on the website will be gone. And then you can also lose a lot of your reputation if there is a SEO spam on the website. For example, if you were ranked in say number five for certain keywords that represent your product on Google search engines, and then suddenly you get hit with SEO spam, then all these search engines then go and visit the website. And all of a sudden they're like, "Oh, there's all these weird key words on here, all this SEO spam that's causing a lot of mixed signals." And the search engines are like, "Oh, where do we rank this website now? Do we rank them with this product that's originally what the website is about? Or do we take into consideration all these other keywords that are mixed up that are SEO spam?" So, all of a sudden your website might go from being ranked number five on the first page to being on the 10th page. And then you rank for all these other keywords that you didn't intend to. And then people search for something completely different. They're searching for jerseys or something, or now they're searching for Prada products, and then suddenly your website pops up in there. So you're not really getting any good traffic, not targeted traffic. But, yeah. Justin Channell: Okay. So in a lot of ways, the effects of SEO spam would kind of be the same for defacements or any kind of malware with the blacklisting, but it does bring that kind of unique part to it where then it can also then bring traffic that you weren't expecting from somebody searching for jerseys, for example. I had not really ever thought about that. Krasimir Konov: Right, right. Yeah. It will definitely bring some traffic. I've seen a lot of times where websites will be connected. Let's say, there was 1,000 websites that were all infected with SEO spam, and it will kind of link each other to try to bring each other up into the rankings. And so you would see a lot of strange traffic from some random websites that were, for example, that were previously infected, even if they might not be anymore. But yeah, they'll be sending traffic to you or there'll be usually search engines sending you traffic, but for the wrong keywords. People are looking for something else, so obviously they're not going to be interested in your website. They're not going to buy anything because they're not looking for that. Justin Channell: And now, so thinking of the way websites get infected, a very common way it seems to be is through phishing campaigns. What are some recommendations you have for the best ways to avoid becoming a phishing victim? Krasimir Konov: Yeah. There is some ways. I mean, it depends really on the type of attack. Obviously, a lot of people, when they think of phishing, they think, "Oh, it's just like a PayPal phishing page and it just looks like the original," but it could be more subtle. If it's just a regular page where you're just going and you get redirected to another website, obviously the first thing to look is if you have the security padlocks, make sure that traffic is encrypted. A lot of these websites don't really have any encryption nowadays. More are starting to get that with pre SSLs being issued and whatnot. But that's the first thing to look and see, make sure. Anywhere you're typing your sensitive information, you want to make sure you have the padlock to make sure everything is encrypted. Krasimir Konov: But also you want to look at the URL of the actual website you're visiting. A lot of times they'll try to hide it. So you might have to be careful and look closely. Something that might be an I will be an L or something like that. And a capital I and L might look kind of similar into your IRL, so you might miss something like that. Say, if you're looking for PayPal and it might replace the L with an I, and if you don't look closely, it might look exactly the same. And you're like, "Oh, okay, it's paypal.com," but not really. So yeah. Just pay attention to the URL, make sure it is the actual website. There's no paypal.com dot something, dot something else, dot com. Yeah. You want it to just say paypal.com, and then it'll have forward slash and something else. But yeah, it gets more complicated when you have, for example, a phishing page that's injected into a regular page. For example, you have a checkout page on a website that you're buying things from and you go through the checkout page and you're looking at where you type in your credit card information and whatnot. And you might have a phishing page that actually looks exactly like a little box that gives you where you put in your credit card number, or your name, your address, and all that. So that will be more subtle. For example, that could be also an I-frame that's just coming from another page. And it will look exactly like it's part of the website. You're on the legitimate website, but only that portion of the website is actually the phishing page. And you look at it and you're like, "Oh, okay. It looks fine. I'm just putting my credentials." So that one could be a lot harder to figure it out. Usually, if it's something like that, I look for something that looks kind of out of place. Maybe they didn't get the right font. It might not be the same as the original website or there might be something out of place, some fields that are missing or some fields that are squished into the left or the right. It looks kind of awkward. It's like, why would this be like this? The whole website looks professional. There's a pink background or something, for example, and then suddenly there's this white box in the middle. It's like, ah, it looks kind of weird, out of place. Justin Channell: So pretty much if anything looks slightly out of place, you really should double check everything at that point. Krasimir Konov: Right. Right. Yeah. Obviously there's more ways that you can check, but I wouldn't get into more technical, like inspecting elements and looking at stuff, but yeah. Justin Channell: And now another type of malware that's kind of, and it kind of plays in with whatever the other infection is, is backdoors. Can you give us some examples of what backdoors can be? It's mainly just when a hacker can get back into the site to reinfect it, but I know there are a ton of different methods. And what are some of the more common ones and then maybe some that really interesting that you've seen? Krasimir Konov: Yeah, there is a lot. They'll probably be one of the first things the hacker would do is if they compromise a website, obviously they'll try to spread backdoors and just inject code everywhere so they can get back in, even if the owner of the website or webmaster cleans it. They want to try and hide some malicious code somewhere so they can always get back in. There's many variations. A backdoor could be something as simple as a single line of code to just [inaudible 00:20:19] argument, some kind of string or something via get or post. Krasimir Konov: And then it runs into an eval, so it evaluates the code and executes it. And some backdoors are very complex and they can be included in, let's say you have a WordPress site and you have a specific login page where all the login credentials are being processed and everything else. They could even inject code into that to basically bypass the whole login mechanism so that they can just bypass everything. They don't even have to know any user. They don't have to know the password, nothing. They'll just include some lines in there, and every time they'll be just able to log in. Yeah. It gets pretty crazy. Yeah. I mean, there's all kinds of malware. There is always a malware, for example, that just targets credit cards and will just target the eCommerce websites. And they'll just try to steal the login credentials, I mean, the credit cards. They'll try to get your address, your credit card information, any kind of CVV code or whatever you typed into the billing address, everything. And then there's also malware like the backdoors that are just trying to keep the attacker in control and trying to get them back into the website. There's just so many variations of what a malicious user might want to do on a website. Some can be something as simple as just reinfecting the website. They don't want to keep control. They just want to keep reinfecting it with some kind of malware. So even if you clean it, it would just get reinfected. Some of them in the database, otherwise might be in the files. We've seen some added into a [inaudible 00:22:14] job that just keeps running on the server. There could be malware that is just a giant to, for example, attack out of websites. Like for example, a distributed denial service where they put the same malware on thousands of websites. And then they try to send traffic to one website to try to bring it down. Yeah. People try to do all kinds of stuff with websites. We've seen even some cryptocurrency mining malware that you go onto a website and suddenly your PC starts running like crazy. And you're like, what the hell is going on? Your fans turn on and the PC is 100% CPU. And it turns out that the website has some malware that's just by mining Bitcoins with your CPU and it's using all of it. Justin Channell: Wow. Okay. So one question now, the last question I have is of all the malware that you've seen, what do you think is the coolest piece of malware that you've ever seen? Krasimir Konov: I think the coolest would be the ones that are so subtle that you don't even know that it's there. For example, we've seen some that were pretty innovative. It will be just a one liner code that's just one line. And for example, it will be let's say 40-50 characters, something like that. And that's all it is. And they'll hide it somewhere in between the legitimate code. And if you don't know what you're looking for, you would never see it. It doesn't look suspicious. There is no links to some other website. There's no some kind of encrypted code or anything like that. It's just a simple one line. And then if you're just scrolling through the file looking for something, you would never see it. It just looks like all the other code. And then if you look closely, you're like, "Oh, there's this..." Look closely, and you're like, "Oh wow, this is not supposed to be there." And then you keep looking at it and you're like, "This looks really weird." And then you see that it's actually doing some malicious things and trying to evaluate some code or taking output from the outside, I mean, some input from outside, you can call it and give it code to run. Justin Channell: Well, Krasimir, thanks for coming on and talking to us for today. Krasimir Konov: Yeah. Thank you. Thank you. I'm so happy. I'm glad I was able to do this podcast and I can't wait to do another one. Justin Channell: Yeah, we'll have you on again. Thanks. Krasimir Konov: Thank you. Justin Channell: Thanks again to Krasimir for joining us here on the Sit Down. We'll be back with another episode next month. So be sure to subscribe on Apple podcasts, Spotify, Stitcher, or any podcasting platform. Also, be sure to follow us on social media at Sucuri Security and check us out at sucuri.net. That's S-U-C-U-R-I.net. I'm Justin Channell, And this has been the Sucuri Sit Down. Stay safe out there.](https://blog.sucuri.net/wp-content/uploads/2020/05/20-sucuri-podcast-blog-post_blog_image-390x183.jpg)
Justin Channell
Rianna MacLeod
Gerson Ruiz