In recent days, a new vulnerability has been found that affects the llhttp parser in the http module in Node v18.7.. This vulnerability, identified as CVE-2022-35256, has been observed to allow HTTP Request Smuggling in certain scenarios that involve improperly terminated header fields. In this post, we will explore what this vulnerability is, how it can be exploited, and what developers can do to prevent attacks that rely on this weakness.

Overview of CVE-2022-35256

The main issue that results in this vulnerability is that the llhttp parser in Node v18.7. does not properly handle header fields that are not terminated with a carriage return and line feed (CRLF) sequence. This oversight in the parser's implementation can create situations where HTTP Request Smuggling becomes possible.

HTTP Request Smuggling is an attack technique that takes advantage of inconsistencies and misinterpretations in parsing or deserializations of HTTP requests. The perpetrator injects a malicious payload that exploits the targeted server's processing algorithms, eventually leading to unauthorized access, denial of service, or bypassing security mechanisms.

Exploiting CVE-2022-35256

To illustrate how this vulnerability can be exploited, let's consider an example where an attacker sends an HTTP request with a malformed header field. This field is not terminated with the CRLF sequence as it should be. Instead, the attacker includes the following payload in the request:

GET / HTTP/1.1
Host: example.com
X-Malicious-Header: SmuggleAttackContent-Length: 42

HTTP/1.1 200 OK
Date: [DATA_HERE]
Content-Type: text/html
Content-Length: [DATA_HERE]
Connection: close

When the llhttp parser encounters this request, it fails to correctly process the X-Malicious-Header field since it is not terminated with a CRFL sequence. Instead, the parser interprets the following characters as part of the same header field:

SmuggleAttackContent-Length: 42

As a result, the parser will fail to detect the actual Content-Length header – allowing the attacker to smuggle their payload into the request. This can lead to a variety of adverse consequences, such as cache poisoning and bypassing security filters.

Mitigating CVE-2022-35256

It's essential for developers using Node v18.7. to be aware of this vulnerability and take appropriate precautions to mitigate the risks posed by it. Some possible ways to address this issue include:

1. Updating Node.js to the latest version, which should contain the necessary fixes for this vulnerability.
2. Employing input validation mechanisms to ensure that incoming HTTP requests are well-formed and contain only valid header fields.
3. Implementing a Web Application Firewall (WAF) that can detect and block attempts to smuggle HTTP requests, as well as other malicious attempts to compromise the application.

For further information on CVE-2022-35256, please consult the original sources

1. Official CVE entry: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-35256
2. Node.js GitHub Repository: https://github.com/nodejs/node/blob/v18.7./lib/_http_parser.js

Conclusion

CVE-2022-35256 highlights the importance of robust input validation and the consequences that can arise from a single oversight in an otherwise secure application. By understanding the vulnerability and taking the necessary steps to mitigate it, developers can protect themselves from potential attacks and ensure their applications run securely and reliably.

Timeline

Published on: 12/05/2022 22:15:00 UTC
Last modified on: 12/08/2022 19:38:00 UTC