Why Do You Need To Be Concerned About HTTP Request Smuggling?


Over the last few months, HTTP request smuggling, the security exploit on the HTTP protocol, has gained extensive community attention. It has happened because of many high-paying bounty reports that have emerged lately. For starters, it is not only about drawing traction. It can prove detrimental based on the configuration set by the servers behind the proxy. Cyber threat actors exploit the HTTP request smuggling vulnerability by meddling with how a website processes a sequence of HTTP requests. Meanwhile, they manipulate any irregularities.


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How Does the Attack Work?

During processing an HTTP request, a server determines the length of HTTP content by directing attention to the content-length or transfer-encoding headers. But the problem emerges when these two headers are available at the same request, thus giving conflicting information. In such a case, a server neglects one of the headers in a bid to avoid a conflict.

However, there remains a possibility that a front-end server might overlook a different header than a back-end server. Thus, it allows an HTTP request smuggling attacker to insert an obscured message by incorporating both headers in a request. The underlying intention is to mislead a back-end server to interpret it as two separate HTTP requests. When one server leaves the end of a malicious HTTP request unprocessed, it adds to the start of the subsequent inbound request.

It is essential to note that the attack works when a back-end server receives multiple requests from a front-end server. Amid many requests, a back-end server struggles to differentiate each request.

The Impact of HTTP Request Smuggling

By smuggling an added request into one, an attacker can wreak havoc on different fronts. For instance, a cybercriminal can obtain access to forbidden resources like site administration. Besides, he can view sensitive data or even hijack the web session of any user.

Things do not end here. A cybercriminal can resort to other attacks as well. It includes cache poisoning, XSS (cross-site scripting) without user interaction, credential hijacking, and firewall protection bypass. For the record, an attacker targets the cache server during a cache poisoning attack. The intention is to show a user a wrong page upon request. Unfortunately, the HTTP request smuggling vulnerability can likewise lead to an account takeover.

How to Block HTTP Request Smuggling?

Often, HTTP request smuggling attacks do not occur on websites refusing to embrace CDNs (content delivery networks), reverse proxies, and load balancers. At the same time, one can overcome the variants of the given vulnerability. It is by configuring the front end of the website to use only HTTP/2 to communicate with the back-end server. The vulnerability also stops posing a threat when you disable the reuse of back-end connections. In addition, it is good to guard sensitive material and administrative web endpoints behind robust authentication mechanisms.

It is also essential to ensure that only administrative users have access to logged HTTP traffic. Hence, potential cyber criminals will have no exposure to unintended parts of an HTTP request.


In simple words, HTTP request smuggling is a hacking technique that targets HTTP devices. Overall, it is a confusing vulnerability to comprehend and so to patch it. An attacker can launch such an attack to achieve a range of malicious objectives. It includes fetching sensitive credentials, hijacking a user’s web sessions, and others. Nonetheless, you can consult LIFARS anytime to take cybersecurity advisory and consulting services to deal with evolving cybersecurity threats.




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