Explanation
Web cache poisoning is a complicated technique whereby an attacker exploits the behavior of an internet server and cache in order that a harmful HTTP response is served to other users.Fundamentally, web cache poisoning involves two phases. First, the attacker must compute the way to elicit a response from the back-end server that inadvertently contains some quite dangerous payload. Once successful, they have to form sure that their response is cached and subsequently served to the intended victims.A poisoned web cache can potentially be a devastating means of distributing numerous different attacks, exploiting vulnerabilities like XSS, JavaScript injection, open redirection, and so on.
How does an internet cache work?To understand how web cache poisoning vulnerabilities arise, it's important to possess a basic understanding of how web caches work.If a server had to send a replacement response to each single HTTP request separately, this is able to likely overload the server, leading to latency issues and a poor user experience, especially during busy periods. Caching is primarily a way of reducing such issues.The cache sits between the server and therefore the user, where it saves (caches) the responses to particular requests, usually for a hard and fast amount of your time . If another user then sends the same request, the cache simply serves a replica of the cached response on to the user, with none interaction from the back-end.
This greatly eases the load on the server by reducing the amount of duplicate requests it's to handle.
Cache keysWhen the cache receives an HTTP request, it first has got to determine whether there's a cached response that it can serve directly, or whether it's to forward the request for handling by the back-end server.
Caches identify equivalent requests by comparing a predefined subset of the request's components, known collectively because the "cache key". Typically, this is able to contain the request line and Host header.
Components of the request that aren't included within the cache key are said to be "unkeyed".If the cache key of an incoming request matches the key of a previous request, then the cache considers them to be equivalent.
As a result, it'll serve a replica of the cached response that was generated for the first request. this is applicable to all or any subsequent requests with the matching cache key, until the cached response expires.Crucially, the opposite components of the request are ignored altogether by the cache. We'll explore the impact of this behavior in additional detail later.
What is the impact of an internet cache poisoning attack?The impact of web cache poisoning is heavily hooked in to two key factors:* What precisely the attacker can successfully get cachedAs the poisoned cache is more a way of distribution than a standalone attack, the impact of web cache poisoning is inextricably linked to how harmful the injected payload is. like most sorts of attack, web cache poisoning also can be utilized in combination with other attacks to escalate the potential impact even further.* The quantity of traffic on the affected pageThe poisoned response will only be served to users who visit the affected page while the cache is poisoned. As a result, the impact can range from non-existent to massive counting on whether the page is popular or not. If an attacker managed to poison a cached response on the house page of a serious website, for instance , the attack could affect thousands of users with none subsequent interaction from the attacker.Note that the duration of a cache entry doesn't necessarily affect the impact of web cache poisoning. An attack can usually be scripted in such how that it re-poisons the cache indefinitely.