CVE-2026-61642
Received Received - Intake

Request Smuggling in Squid Proxy via HTTP/1.1 Transfer-Encoding

Publication date: 2026-10-13

Last updated on: 2026-10-13

Assigner: GitHub, Inc.

Description
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.

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Meta Information

Published
2026-10-13
Last Modified
2026-10-13
Generated
2026-10-13
AI Q&A
2026-10-13
EPSS Evaluated
N/A
NVD
CVE-2026-61642
EUVD
EUVD-2026-98919

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
squid-cache squid >= 3.3.0.1, < 7.6

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-444 The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

Attack-Flow Graph

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Executive Summary

This vulnerability in Squid versions 3.3.0.1 to before 7.6 allows a Request Smuggling attack due to improper enforcement of HTTP/1.1 Transfer-Encoding rules. The issue occurs because Squid incorrectly accepts a bare 'Transfer-Encoding: identity' header, which violates HTTP specifications. This enables a trusted client to bypass security mechanisms and smuggle requests.

Detection Guidance

Detecting this vulnerability requires checking the Squid proxy version and inspecting HTTP traffic for malformed Transfer-Encoding headers. Use 'squid -v' to verify the installed version. If the version is below 7.6, the system is vulnerable. Monitor HTTP requests for 'Transfer-Encoding: identity' headers, which violate HTTP/1.1 specifications.

Impact Analysis

If exploited, this vulnerability could allow an attacker to bypass security controls between the client and Squid. In environments with an HTTP cache before Squid, it may enable cache poisoning, where malicious content is stored at any URL and delivered to other users' requests.

Mitigation Strategies

Upgrade Squid to version 7.6 or later immediately. If upgrading is not possible, disable HTTP/1.1 support or configure strict header validation in Squid's configuration. Additionally, review and update firewall rules to block suspicious Transfer-Encoding headers.

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