CVE-2026-61642: Request Smuggling (CVSS 7.7)

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.

Is your site exposed to CVE-2026-61642?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

7.7

HIGH

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

EPSS — Exploit Prediction

0.0468

Probability of exploitation

0.92%

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/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

Frequently Asked Questions

What is CVE-2026-61642? +

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. It has a CVSS v3.1 base score of 7.7 (HIGH).

How severe is CVE-2026-61642? +

CVE-2026-61642 has a CVSS v3.1 score of 7.7 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0468, placing it in the 1th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-61642? +

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.

Related Vulnerabilities

CVE-2025-1867

Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in ithewei libhv allows HTTP Response Smuggling.This issue affects libhv: through …

CVE-2024-23316

HTTP request desynchronization in Ping Identity PingAccess, all versions prior to 8.0.1 affected allows an attacker to send specially crafted …

CVE-2024-38494

This vulnerability allows a high-privileged authenticated PAM user to achieve remote command execution on the affected PAM system by sending …

CVE-2025-6999

An HTTP Request Smuggling [CWE-444] vulnerability in the Authentication portal of WatchGuard Fireware OS allows a remote attacker to evade …

CVE-2025-11915

Connection desynchronization between an HTTP proxy and the model backend. The fixes were rolled out for all proxies in front …

CVE-2023-53878

Member Login Script 3.3 contains a client-side desynchronization vulnerability that allows attackers to manipulate HTTP request handling by exploiting Content-Length …

CVE-2026-61642