Squid <7.5 Heap UAF DoS via ICP
CVE-2026-33526 Published on March 26, 2026
Squid vulnerable to Denial of Service in ICP Request handling
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.
Vulnerability Analysis
CVE-2026-33526 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Types
What is a Dangling pointer Vulnerability?
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.
CVE-2026-33526 has been classified to as a Dangling pointer vulnerability or weakness.
Premature Release of Resource During Expected Lifetime
The program releases a resource that is still intended to be used by the program itself or another actor.
What is a Dangling pointer Vulnerability?
The program dereferences a pointer that contains a location for memory that was previously valid, but is no longer valid. When a program releases memory, but it maintains a pointer to that memory, then the memory might be re-allocated at a later time. If the original pointer is accessed to read or write data, then this could cause the program to read or modify data that is in use by a different function or process. Depending on how the newly-allocated memory is used, this could lead to a denial of service, information exposure, or code execution.
CVE-2026-33526 has been classified to as a Dangling pointer vulnerability or weakness.
Products Associated with CVE-2026-33526
You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-33526 are published in these products:
Affected Versions
squid-cache squid:- Version < 7.5 is affected.
- Version 7:6.10-6.el10_1.3 and below * is unaffected.
- Version 7:6.10-5.el10_0.2 and below * is unaffected.
- Version 7:3.5.20-17.el7_9.16 and below * is unaffected.
- Version 8100020260408092701.489197e6 and below * is unaffected.
- Version 8040020260514123440.522a0ee4 and below * is unaffected.
- Version 8040020260514123440.522a0ee4 and below * is unaffected.
- Version 8060020260518090356.ad008a3a and below * is unaffected.
- Version 8060020260518090356.ad008a3a and below * is unaffected.
- Version 8060020260518090356.ad008a3a and below * is unaffected.
- Version 8080020260514105733.63b34585 and below * is unaffected.
- Version 8080020260514105733.63b34585 and below * is unaffected.
- Version 7:5.5-22.el9_7.4 and below * is unaffected.
- Version 7:5.2-1.el9_0.10 and below * is unaffected.
- Version 7:5.5-5.el9_2.11 and below * is unaffected.
- Version 7:5.5-13.el9_4.5 and below * is unaffected.
- Version 7:5.5-19.el9_6.3 and below * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.