Vulnerability · Published Jun 17, 2026 · Assigned by VulnCheck

CVE-2026-54388Tinyproxy - HTTP Request Smuggling via Duplicate Content-Length Headers

Critical 9.1

In plain English

A critical-severity security flaw in tinyproxy from tinyproxy. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities).

Severity (CVSS 3.1)9.1Critical

Exploit odds (30 days)0.4%top 61.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:14	tinyproxy	no fix listed	DEBIAN-CVE-2026-54388
Ubuntu:24.04:LTS	tinyproxy	no fix listed	UBUNTU-CVE-2026-54388
Ubuntu:25.10	tinyproxy	no fix listed	UBUNTU-CVE-2026-54388
Ubuntu:26.04:LTS	tinyproxy	no fix listed	UBUNTU-CVE-2026-54388
Ubuntu:26.10	tinyproxy	no fix listed	UBUNTU-CVE-2026-54388

Affected products (as reported)

Vendor	Product	Versions
tinyproxy	tinyproxy	0 – through 1.11.3

Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References

Researcher Pull Request issue-tracking
Maintainer Pull Request issue-tracking
Patch Commit patch
https://www.vulncheck.com/advisories/tinyproxy-http-request-smuggling-via-duplicate-content-length-headers third-party-advisory