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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.

PUBLISHED Reserved 2026-06-12 | Published 2026-06-17 | Updated 2026-06-23 | Assigner VulnCheck




CRITICAL: 9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CRITICAL: 9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Problem types

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Product status

Default status
affected

Any version
affected

364cdb67e0ea00a8e4a7037e2693e0711e816adb (git)
unaffected

Credits

Tristan Madani (@TristanInSec) finder

References

github.com/tinyproxy/tinyproxy/issues/609 exploit

github.com/tinyproxy/tinyproxy/issues/609 (Researcher Pull Request) issue-tracking

github.com/tinyproxy/tinyproxy/pull/610 (Maintainer Pull Request) issue-tracking

github.com/...ommit/364cdb67e0ea00a8e4a7037e2693e0711e816adb (Patch Commit) patch

www.vulncheck.com/...ng-via-duplicate-content-length-headers third-party-advisory

cve.org (CVE-2026-54388)

nvd.nist.gov (CVE-2026-54388)

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