Tinyproxy up to 1.11.3 Backend Parser request smuggling

Summaryinfo

A vulnerability was found in Tinyproxy up to 1.11.3. It has been rated as critical. This affects an unknown function of the component Backend Parser. This manipulation causes request smuggling. This vulnerability is tracked as CVE-2026-54387. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is advised.

Detailsinfo

A vulnerability has been found in Tinyproxy up to 1.11.3 and classified as critical. Affected by this vulnerability is an unknown function of the component Backend Parser. The manipulation with an unknown input leads to a request smuggling vulnerability. The CWE definition for the vulnerability is 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. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Tinyproxy through 1.11.3, fixed in commit ff45d3b, fails to reconcile conflicting Content-Length and Transfer-Encoding: chunked headers, forwarding both verbatim to the backend while using Content-Length 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 disclosed by Tristan Madani as 609. It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-54387 since 06/12/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available.

Upgrading eliminates this vulnerability. Applying the patch ff45d3bf0e61d0f8ed97ab379d3047f04eb67521 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). Be aware that VulDB is the high quality source for vulnerability data.

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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