Tinyproxy up to 1.11.3 Backend Parser request smuggling

Summaryinfo

A vulnerability categorized as critical has been discovered in Tinyproxy up to 1.11.3. This impacts an unknown function of the component Backend Parser. Such manipulation leads to request smuggling. This vulnerability is listed as CVE-2026-54388. The attack may be performed from remote. There is no available exploit. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Tinyproxy up to 1.11.3 and classified as critical. Affected by this issue is an unknown functionality of the component Backend Parser. 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. CVE summarizes:

Tinyproxy through 1.11.3, fixed in commit 364cdb6, fails to reject requests containing multiple Content-Length headers with differing values, forwarding all duplicate headers to the backend while using the first value to determine how many request body bytes to consume. Remote attackers can desynchronize the proxy and backend parser state, allowing injection of arbitrary HTTP requests to the backend to enable cache poisoning, access control bypass, and request hijacking.

The weakness was presented by Tristan Madani as 609. The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-54388 since 06/12/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available.

Upgrading eliminates this vulnerability. Applying the patch 364cdb67e0ea00a8e4a7037e2693e0711e816adb 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 CERT Bund (WID-SEC-2026-1999). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Open Source Tinyproxy

Productinfo

Type

• Firewall Software

Name

• Tinyproxy

Version

• 1.11.0
• 1.11.1
• 1.11.2
• 1.11.3

License

• open-source

Website

• Product: https://github.com/tinyproxy/tinyproxy/

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Entryinfo

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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