Imagine for a moment that you’re searching for a topic. You find what you’re looking for on the first page of the search results and click through to the website. But instead of the expected web page, you find yourself staring down the barrel of a 503: Service Unavailable error message.
You’re going to immediately click back and navigate to the next result, right?
More often than not, a visitor confronted with a 503 status code will immediately return to the search results and go somewhere else. 503 errors can lead to confusion and frustration for users — and may have a long-lasting impact on your traffic.
To make matters more complicated, there are a wide range of different problems that can lead to 503 errors on your website.
There’s no 100% quick and easy fix to resolve 503 errors on your site. Errors happen due to plugin conflicts, unexpected maintenance, and connection floods that take the server down. It will take a bit of digging to find out the source.
In today’s post, we’ll be exploring the ins and outs of 503 errors to uncover what they mean for your site and traffic. We’ll also explore what causes them and how to fix 503s on your website.
Contents:
- What is HTTP error 503?
- How to fix a 503 Service Unavailable error
- Malware & 503 server errors
- DDoS & 503: Service Unavailable errors
- Do 503 errors impact SEO?
What is an HTTP 503 error?
In simple terms, an HTTP 503 error indicates your site can’t be reached because your server isn’t available. This response code can occur if your website is too busy or under maintenance. You may also receive a 503 if your site is experiencing a DDoS attack or something else that requires further investigation.
The Internet Engineering Task Force defines the 503 Service Unavailable error as follows:
The 503 (Service Unavailable) status code indicates that the server is currently unable to handle the request due to a temporary overload or scheduled maintenance, which will likely be alleviated after some delay. The server MAY send a Retry-After header field to suggest an appropriate amount of time for the client to wait before retrying the request.
The most frustrating thing about a 503 error code is that very little information is given to you to work with. Even though 503 errors help you identify a problem with server availability, they won’t tell you the reason for it happening. Most times, you’ll just find a “Service temporarily unavailable” message.
Status Codes: 503 Error
503 error codes come in different shapes and sizes, but they mean the same thing. Here are a few different variations you might encounter in your browser.
- 503 Service Unavailable
- http/1.1 Service Unavailable
- HTTP Server Error 503
- 503 Error
- HTTP 503
- HTTP Error 503
Now that we’re familiar with some of the different naming conventions for 503 errors, let’s take a look at how to fix them.
How are 503 errors different from other internal server errors?
There are many types of internal server status error codes and they all mean different things.
To help you understand the difference between generic 500 errors and other types of internal server errors, we’ve outlined some of the common types of 5xx responses you might encounter on your site.
- 500 error: server encountered an unexpected problem. This error code comes up when something unexpected happens on the server which prevents it from completing the request, but no additional information is shown.
- 501 error: HTTP status code for not implemented. This indicates that the server is unable to execute the request and is either unable to identify the goal of the request, or does not have enough power to execute the request.
- 502 error: bad gateway. Essentially, an invalid response was detected. The server was doing a job as a proxy or a gateway and received an invalid response from a different upstream server. If you are using a WAF, this could indicate a problem with your server.
- 503 error: a service is unavailable. This occurs when the server gets too many tasks and is overloaded, down due to maintenance, or has been taken down by malware.
- 504 error: Gateway timeout. The server, which was performing as a proxy or a gateway, wasn’t able to identify the request within the fixed time limit.
- 505 error: HTTP version not supported by server. The server isn’t able to identify the HTTP protocol used in the request.
- 511 error: network authentication. The server requires user authentication to access the request.
With the exception of a 500 error, the majority of server errors provide clear reasons for the status response that can help you pinpoint the issue and resolve it.
But don’t despair; there are a number of potential causes for the vague and generic 500 server error. Let’s examine some of these sources before we move on to possible solutions.
How to fix a 503: Service Unavailable error
Since you won’t always know what has caused the 503 error, we’re going to need to do some methodical troubleshooting to pinpoint the root cause.
Here are eight steps to help resolve a 503 error on your website. Remember to refresh your web page before and after trying any of these steps.
1. Check to see if your server is going through maintenance.
Almost all web servers shut down when they’re going through maintenance. To rule out the possibility of 503 errors due to maintenance, check your server’s configuration options to see when automatic maintenance sessions are scheduled. If any updates need to be applied to your site, we recommend that you schedule them when your site’s traffic is lowest so that your visitors don’t encounter these errors.
2. Look through your server and application logs.
Server logs give you information about the hardware that is running your server and also reveal details about its status and health. And application logs recount your website’s full history. These important logs also allow you to see the web pages requested by visitors, and the servers they are connected to. You’ll want to review all of your logs files to identify any suspicious details that may be lurking server-side.
3. Review code for bugs and recent file modifications.
If there’s an error in your website’s plugins, or theme files, your web server might not be able to correctly answer or respond to requests. In fact, plugin conflicts and misconfigured web applications are a known cause of 503 errors. So you’ll want to examine your website code for any recent changes or bugs that may be causing the problem on your site. If you have file integrity monitoring in place or are able to review recent changes and modifications to your website, you may be able to pinpoint the situation and root cause of the issue and revert back to a last known good configuration.
4. Enable WP_DEBUG in WordPress.
WordPress websites come bundled with a debug tool that makes it easy to see root causes for website errors – a feature known as WP_DEBUG. Try securely activating debugging on WordPress then review your logs to troubleshoot and pinpoint the cause of the error.
If you see 503 errors in WordPress, this feature can save a lot of troubleshooting cycles. The results of debug mode will be found in your debug.log file.
5. Increase your server resources.
A 503 error is often a sign that your website is under temporary overload. Contact your web host to discuss the 503 error and let them know which steps you’ve already tried. If recurring HTTP 503 errors are regularly caused by traffic spikes, it is advisable to increase your web server resources investment. Try upgrading your hosting plan to see if that resolves the issue.
6. Try a server reboot.
Sometimes, congestion builds up in the server chain hosting your website. One of the quickest methods to troubleshoot a 503 error is to refresh your server and restart your web browser. If your website happens to be hosted on a number of servers, please ensure you restart all of them to get them up and running again.
7. Use a web application firewall.
A server overload can be caused by a DDoS attack which floods your server’s resources and takes your website offline, resulting in a 503 error. Set up a website firewall to help block fake traffic and malicious bots, mitigating the effects of a DDoS attack in the process.
WAFs and CDNs often serve used digital resources from its own cache relieving load on the hosting server, either due to a DDoS attack or a general lack of server resources such as processor and memory.
Refer to our post on how to know if you’re under DDoS attack for more details on troubleshooting this step, or check out this video below on how to identify and stop DDoS.
8. Scan for malware.
In some cases, SEO spam, infected plugins or themes, or even cryptomining malware can cause 503 errors on your website. You’ll want to perform an extensive scan of your website’s files and server to rule out a compromise or infection causing the error.
Remember: If your site is undergoing scheduled maintenance, a 503 Service Unavailable status is precisely what you want on your website until maintenance is done. But if left untreated long-term, it can have harmful effects on SEO.
Most importantly, you’ll want to fix site errors as soon as they’re detected. If visitors find an error when they navigate to your web page, they’ll be less likely to return to your site in the future.
Pro tip: Set up website monitoring to be notified of future issues, server errors, and other indicators of compromise on your web pages.
How does malware cause 503 server errors?
Any malware that overloads the server can lead to 503 errors. For example, cryptominer malware is designed to abuse the resources and often results in maxed out CPU. As resources are hogged to mine crypto currency instead of keeping your website online, visitors will be unable to establish a connection with the server. This leads to 503 errors on your site.
SEO spam is another example of malware that can result in HTTP 503 errors. Many spam infections create thousands of spammy URLs on the victim website, marketing things like pharmaceuticals, essay writing services, and other spam content.
These URLs get indexed by search engines like Google and become lodged within search results. Even after the SEO spam infection is removed, search engines will continue to attempt to index the spam pages. Since the malicious spam pages may number in the tens (or even sometimes hundreds) of thousands, it can cause the website to go completely offline.
Eventually the spam URLs will disappear, but it typically takes a few weeks (sometimes longer) before that occurs.
How does DDoS result in 503: Service Unavailable errors?
An HTTP 503 error is a sign that your origin web server has been temporarily overloaded. And since DDoS attacks overwhelm and disrupt normal operations and website functionality, the most immediate and obvious impact is that your server resources are overwhelmed. Your website may be unavailable as a result, leading to HTTP 503 errors in your browser.
Do 503 errors impact SEO?
A 503: Service Unavailable status is exactly what a website administrator should return when a site is undergoing scheduled maintenance. When Google bot encounters a 503 error, it knows to come back later on to check the page. But if over time search engine bots continue to encounter the error, it will understand that the problem is not temporary and remove the page from its index.
Because they affect the user experience directly, 503 error codes can be harmful to your SEO. Any long-term 503 errors will have a direct impact on your website rankings. So if you’re experiencing 503’s over a long duration, you’ll want to sort out the issue to prevent problems.
Identifying the root cause of 503 errors
The 503 error can cause a lot of disruption for your website. But with a bit of luck, your 503 error was merely the result of a scheduled maintenance and these instructions were able to help you get quickly back online.
To identify the root cause of a 503 error, follow these troubleshooting steps:
- Check to see if your server is going through maintenance.
- Look through your server and application logs.
- Review code for bugs and recent file modifications.
- Enable WP_DEBUG in WordPress.
- Increase your server resources.
- Try a server reboot.
- Use a web application firewall.
- Scan for malware.
If you have detected a DDoS attack or website malware as the culprit and you need a hand tackling the problem, we’re here to help. We can help safely remove malicious code found in your website file system and server, mitigate DDoS attacks, and get your site back online.
Art Martori
Denis Sinegubko![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
Stephen Johnston
Rianna MacLeod
Ben Martin
Luke Leal
Marc Kranat
Kyle Knight