Squid is a caching proxy for the Web. From 3.3.0.1 to before 7.6, due to an improper enforcement of behavioral workflow bug, Squid is vulnerable to a Request Smuggling attack against HTTP/1.1 Transfer-Encoding. HTTP header parsing (`src/HttpHeader.cc`) accepted the bare` Transfer-Encoding:` identity form, which the HTTP specification prohibits because any transfer coding must be wrapped within chunked encoding. This problem allows a trusted client to perform an HTTP Request Smuggling attack when HTTP/1.1 is used, bypassing security mechanisms that may be in place between attacker and Squid. When there is an HTTP cache operating prior to the affected Squid, this Request Smuggling attack also allows the attacker to poison that web cache and store arbitrary malicious content at any URL for delivery to other clients' future requests. This issue is fixed in version 7.6.
Fix
Microsoft's update · Important
- Release Notes — azl3 squid 6.13-5 on Azure Linux 3.0 · build 6.13-6
From the 2026-Oct release note of Microsoft's Security Update Guide, revised 2026-10-29.
Vendor advisories in the News 1
- USN-8941-1: Squid vulnerabilities Ubuntu Security Notices · 2026-10-20
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 2
- StatusReceived → Awaiting AnalysisNVD modified 2026-10-16 16:00
- First seenCVSS 7.7NVD modified 2026-10-13 18:17
Affected (CPE criteria) 0
NVD has not attached CPE configurations yet.
References 6
- https://github.com/squid-cache/squid/commit/d06f48de8b8cc9a378cb91ecfe8e89b6e81696d2
- https://github.com/squid-cache/squid/commit/d808a7c825a70275113790471135c9c4d547ee51
- https://github.com/squid-cache/squid/pull/2427
- https://github.com/squid-cache/squid/pull/2431
- https://github.com/squid-cache/squid/releases/tag/SQUID_7_6
- https://github.com/squid-cache/squid/security/advisories/GHSA-537g-4gfh-w7m6