mtrudel bandit up to 1.10.x HTTP Request lib/bandit/headers.ex Elixir.bandit.Headers:get_content_length request smuggling

Summaryinfo

A vulnerability marked as critical has been reported in mtrudel bandit up to 1.10.x. This affects the function Elixir.bandit.Headers:get_content_length in the library lib/bandit/headers.ex of the component HTTP Request Handler. The manipulation leads to request smuggling. This vulnerability is documented as CVE-2026-39805. The attack can be initiated remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability was found in mtrudel bandit up to 1.10.x. It has been rated as critical. This issue affects the function Elixir.bandit.Headers:get_content_length in the library lib/bandit/headers.ex of the component HTTP Request Handler. The manipulation with an unknown input leads to a request smuggling vulnerability. Using CWE to declare the problem leads to CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Inconsistent Interpretation of HTTP Requests vulnerability in mtrudel bandit allows HTTP request smuggling via duplicate Content-Length headers. 'Elixir.Bandit.Headers':get_content_length/1 in lib/bandit/headers.ex uses List.keyfind/3, which returns only the first matching header. When a request contains two Content-Length headers with different values, Bandit silently accepts it, uses the first value to read the body, and dispatches the remaining bytes as a second pipelined request on the same keep-alive connection. RFC 9112 §6.3 requires recipients to treat this as an unrecoverable framing error. When Bandit sits behind a proxy that picks the last Content-Length value and forwards the request rather than rejecting it, an unauthenticated attacker can smuggle requests past edge WAF rules, path-based ACLs, rate limiting, and audit logging. This issue affects bandit: before 1.11.0.

The weakness was released by Peter Ullrich and Jonatan Männchen as GHSA-c67r-gc9j-2qf7. It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-39805 since 04/07/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 1.11.0 eliminates this vulnerability. Applying the patch f2ca636eb6df385219957e8934e9fc6efa1630d1 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-26712). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Vendor

• mtrudel

Name

• bandit

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10

License

• open-source

Website

• Product: https://github.com/mtrudel/bandit/

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