CVE-2026-54388: Request Smuggling (CVSS 9.1)

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.

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CVSS v3.1 Score

9.1

CRITICAL

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

EPSS — Exploit Prediction

0.0044

Probability of exploitation

0.36%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-444 CWE-444

References

Other 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

Frequently Asked Questions

What is CVE-2026-54388? +

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. It has a CVSS v3.1 base score of 9.1 (CRITICAL).

How severe is CVE-2026-54388? +

CVE-2026-54388 has a CVSS v3.1 score of 9.1 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0044, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-54388? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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CVE-2026-54388