CVE-2026-54388 Tinyproxy - HTTP Request Smuggling via Duplicate Content-Length Headers
Remote attackers can desynchronize proxy and backend parsers via duplicate Content-Length headers, enabling request injection, cache poisoning, and access control bypass.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-54388?
CVE-2026-54388 is a critical vulnerability in tinyproxy, published on 17 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-444
Which versions are affected by CVE-2026-54388?
How do I fix CVE-2026-54388?
Apply the vendor's patch.
Is CVE-2026-54388 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54388 exists.
Sources
Also known as DEBIAN-CVE-2026-54388, GHSA-p3h9-73g9-x6m3, UBUNTU-CVE-2026-54388.