CVE-2026-33526: squid-cache squid Use After Free

Vulnerability summary

CVE-2026-33526 is a critical (CVSS 9.2) Use After Free vulnerability in squid-cache squid. EPSS estimates a 8.94% chance of exploitation in the next 30 days, higher than 95.2% of scored vulnerabilities.

Timeline

1. 26-03-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

Description

Squid is a caching proxy for the Web. Prior to version 7.5, due to heap Use-After-Free, Squid is vulnerable to Denial of Service when handling ICP traffic. This problem allows a remote attacker to perform a reliable and repeatable Denial of Service attack against the Squid service using ICP protocol. This attack is limited to Squid deployments that explicitly enable ICP support (i.e. configure non-zero `icp_port`). This problem _cannot_ be mitigated by denying ICP queries using `icp_access` rules. Version 7.5 contains a patch.

• CWE-416Use After FreeThe product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.
• CWE-826Premature Release of Resource During Expected LifetimeThe product releases a resource that is still intended to be used by itself or another actor.
• CWE-825Expired Pointer DereferenceThe product dereferences a pointer that contains a location for memory that was previously valid, but is no longer valid.