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

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-17 · updated 2026-07-14
Weakness: CWE-444

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 products

tinyproxy: through 1.11.3

References

https://github.com/tinyproxy/tinyproxy/commit/364cdb67e0ea00a8e4a7037e2693e0711e816adb
https://github.com/tinyproxy/tinyproxy/issues/609
https://github.com/tinyproxy/tinyproxy/pull/610
https://www.vulncheck.com/advisories/tinyproxy-http-request-smuggling-via-duplicate-content-length-headers
https://github.com/tinyproxy/tinyproxy/issues/609

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