Preventing cache poisoning attacks 

If you have a website or a web application, you know you should be guarding them against attack. Many security measures focus on attacks that directly exploit vulnerabilities in the site or app themselves, but there is also a significant risk of attack on caches. When you’re online, caches are used to speed up interactions. While this is great for your user experience, it is also a potential attack vector. 

Your website and applications are at risk of cache poisoning, an attack leveraged on their cache using injection tactics. It’s not an easy attack to catch, but with the right tools, you can prevent and mitigate attacks, saving yourself a great deal of issues down the line.  

What is cache poisoning? 

Caches, a server or browser’s way of temporarily storing information for quick access later, are susceptible to malicious attacks known as cache poisoning. Cache poisoning occurs when an attacker alters the information stored in the cache so that it negatively impacts the user. Some users experience data loss or theft, and others have reported encountering malware. Another common result of cache poisoning is redirection to a fraudulent website or application. 

There are a few different types of cache poisoning, including DNS spoofing and web cache poisoning. In DNS spoofing, the attackers impersonate legitimate websites and respond to queries with malicious content rather than the appropriate cache content. This can lead to customers downloading malware and experiencing data theft. 

Web cache poisoning works a little differently. Instead of impersonating another website, this attack sends a request that results in the cache storing malicious content. This content is then pushed out to users who send subsequent requests. In some cases, the attack forces the cache to store too much content, which can create a Denial of Service attack and prevent access to a website or server. 

Mitigating cache poisoning attacks 

One of the reasons cache poisoning attacks are so insidious is that they are difficult to detect, which allows them to slip past many of your security tools. Cache poisoning targets both your website or application and your customers’ devices, which makes them a big problem that can be challenging to solve.  

However, there are some best practices and tools that you can use to mitigate these attacks. 

• Normalization. Cache key normalization reduces variability in handling requests. By enforcing standards for processing and limiting the number of potential variations, more precise cache keys are generated. This means that it is more difficult for attackers to insert malicious content. 

• Cache-control header use. Normally, a developer would provide instructions for caching. HTTP headers provide directions for storage, and it’s possible to use these headers to exert tighter control over what content is delivered to the end user following a request.  

• Validation and sanitization. When malicious users provide data to be cached, cache poisoning occurs via carefully tweaked requests. There may be a line of code in the request that inserts malicious content into the cache, or it may redirect future users to a different website. Either way, validating and sanitizing inputs can eliminate these unexpected (and unwanted) instructions. 

• WAF implementation. One of the simplest ways to prevent cache poisoning is to use tools that automatically monitor, detect, and respond to unusual activity. A web application firewall (WAF) is able to block unusual activity based on customizable rules. DNS spoofing and web cache poisoning both have known attack patterns that a WAF will recognize and block before they can infect the cache. 

• Encryption. Adopting HTTPS and other encryption protocols serves two functions. Firstly, it prevents attackers from viewing sensitive data. Secondly, it makes it more difficult to insert malicious content into a cache because it limits the amount of information (including code) that an attacker can see and later leverage.  

While it’s not possible to guarantee immunity from cache poisoning, using these tools and best practices can eliminate the majority of attacks, reducing your risk of infection. This benefits both you and your customers as the customers will be protected from data theft, malware infection, and other ill effects. However, once you have reduced your risk, it’s important to take steps to secure your caching systems so that adapting attackers don’t get ahead of you. 

Securing caching systems 

Cache poisoning can be detrimental to your organization, and it can seriously harm your customers. A successful attack can cause your legitimate website to be inaccessible, or it might redirect your customers to an illegitimate website that deposits malware on their devices. Neither outcome will do any service to your reputation. 

WAFs can help with mitigating cache poisoning attacks, but they can also help secure your caching systems long-term by preventing illegitimate access. When you use a WAF, you have traffic analysis and alerts that offer early detection of suspicious activity at potential points of entry for attackers. Some WAF solutions are able to use machine learning-informed algorithms to detect unknown attacks. Historically, WAFs have been optimized to detect and block known attack patterns, so this development is highly beneficial to your security environment.  

Cache poisoning is a relatively subtle attack, but it can have devastating impacts if it is not caught quickly, both for you and for your customers. Fortunately, there are ways to mitigate these attacks and secure your systems, and using the right tools, like a WAF solution, can vastly improve your security.