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Squid CVE-2026-33526

| EUVDEUVD-2026-16068 CRITICAL
Use After Free (CWE-416)
2026-03-26 GitHub_M
Denial Of Service Use After Free Memory Corruption Squid
Critical
Disputed · 9.2 Vendor: GitHub_M
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Severity by source

Sources disagree (Medium–Critical)
Vendor (GitHub_M) PRIMARY
9.2 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Ubuntu
MEDIUM
qualitative
SUSE
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Red Hat
7.5 HIGH
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorVendor: GitHub_M

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

4
Patch released
Mar 31, 2026 - 21:13 nvd
Patch available
EUVD ID Assigned
Mar 26, 2026 - 01:00 euvd
EUVD-2026-16068
Analysis Generated
Mar 26, 2026 - 01:00 vuln.today
CVE Published
Mar 26, 2026 - 00:16 nvd
CRITICAL 9.2

DescriptionCVE.org

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.

AnalysisAI

Squid versions prior to 7.5 contain a heap use-after-free vulnerability (CWE-416) in ICP (Internet Cache Protocol) traffic handling that enables remote attackers to reliably trigger denial of service against affected proxy services. The vulnerability affects any Squid deployment with ICP support explicitly enabled via non-zero icp_port configuration, and cannot be mitigated through access control rules alone. A patch is available in version 7.5, and the vulnerability has been confirmed across multiple Debian releases and SUSE distributions.

Technical ContextAI

The vulnerability resides in Squid's ICP protocol implementation, a lightweight UDP-based cache discovery and querying protocol commonly used in distributed caching architectures. The root cause is a heap use-after-free condition (CWE-416) triggered during ICP packet processing, where memory is referenced after being freed, leading to memory corruption. The affected component is the ICP message handler in Squid's network stack, which processes incoming ICP queries on the configured icp_port. The CPE string cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:* indicates all Squid versions across all release branches are potentially affected up to the patched 7.5 version. This memory safety issue occurs at the protocol parsing level, making it exploitable remotely without authentication.

RemediationAI

Upgrade Squid to version 7.5 or later, which includes the upstream patch (commit 8a7d42f9d44befb8fcbbb619505587c8de6a1e91). For systems unable to patch immediately, the only reliable mitigation is to disable ICP support by setting icp_port to 0 in squid.conf and restarting the service, though this may impact cache peering if ICP is in use. Organizations should prioritize patching since access control rules (icp_access) do not mitigate this memory corruption vulnerability. Consult your Linux distribution (Debian, SUSE, etc.) for backported packages, and verify patch application via version checking (squid -v) and testing ICP functionality is restored or disabled as intended.

More in Squid

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Squid is vulnerable to a Denial of Service, where a remote attacker can perform buffer overflow attack by writing up to

CVE-2016-4054 HIGH
8.1 Apr 25

Buffer overflow in Squid 3.x before 3.5.17 and 4.x before 4.0.9 allows remote attackers to execute arbitrary code via cr
CVE-2016-4555 HIGH POC
7.5 May 10

client_side_request.cc in Squid 3.x before 3.5.18 and 4.x before 4.0.10 allows remote servers to cause a denial of servi
CVE-2016-3947 HIGH
8.2 Apr 07

Heap-based buffer overflow in the Icmp6::Recv function in icmp/Icmp6.cc in the pinger utility in Squid before 3.5.16 and
CVE-2013-4123 MEDIUM POC
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client_side_request.cc in Squid 3.2.x before 3.2.13 and 3.3.x before 3.3.8 allows remote attackers to cause a denial of

CVE-2013-4115 HIGH
7.5 Aug 09

Buffer overflow in the idnsALookup function in dns_internal.cc in Squid 3.2 through 3.2.11 and 3.3 through 3.3.6 allows

CVE-2016-4554 HIGH
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mime_header.cc in Squid before 3.5.18 allows remote attackers to bypass intended same-origin restrictions and possibly c
CVE-2014-7141 MEDIUM
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The pinger in Squid 3.x before 3.4.8 allows remote attackers to obtain sensitive information or cause a denial of servic
CVE-2014-3609 MEDIUM
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HttpHdrRange.cc in Squid 3.x before 3.3.12 and 3.4.x before 3.4.6 allows remote attackers to cause a denial of service (
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7.5 Feb 27

Squid 3.x before 3.5.15 and 4.x before 4.0.7 does not properly append data to String objects, which allows remote server
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Squid 3.x before 3.5.16 and 4.x before 4.0.8 improperly perform bounds checking, which allows remote attackers to cause

Same weakness CWE-416 – Use After Free

View all
CVE-2019-0708 CRITICAL POC
9.8
CVE-2015-5119 CRITICAL POC
9.8
CVE-2014-0322 HIGH POC
8.8
CVE-2012-4792 HIGH POC
8.8
CVE-2009-4324 HIGH POC
7.8
CVE-2015-0313 CRITICAL POC
9.8
CVE-2015-5122 CRITICAL POC
9.8
CVE-2013-2551 HIGH POC
8.8

Same technique Denial Of Service

View all
CVE-2015-5119 CRITICAL POC
9.8
CVE-2011-2462 CRITICAL POC
9.8
CVE-2011-0611 HIGH POC
8.8
CVE-2012-1889 HIGH POC
8.8
CVE-2012-0507 CRITICAL POC
9.8
CVE-2014-1761 HIGH POC
7.8
CVE-2015-5122 CRITICAL POC
9.8
CVE-2011-0609 HIGH POC
7.8

Vendor StatusVendor

Ubuntu

Priority: Medium
squid
Release Status Version
focal needs-triage -
jammy needs-triage -
noble needs-triage -
questing needs-triage -
upstream needs-triage -
squid3
Release Status Version
xenial needs-triage -
bionic needs-triage -
jammy DNE -
noble DNE -
questing DNE -
upstream needs-triage -

Debian

squid
Release Status Fixed Version Urgency
bullseye vulnerable 4.13-10+deb11u3 -
bullseye (security) vulnerable 4.13-10+deb11u6 -
bookworm vulnerable 5.7-2+deb12u5 -
bookworm (security) vulnerable 5.7-2+deb12u4 -
trixie, trixie (security) vulnerable 6.13-2+deb13u1 -
forky vulnerable 7.4-1 -
sid fixed 7.5-1 -
(unstable) fixed 7.5-1 -

SUSE

Severity: High
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Server 15 SP7 Fixed
SUSE Linux Enterprise Server 16.0 Fixed
SUSE Linux Enterprise Server 16.1 Fixed

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CVE-2026-33526 vulnerability details – vuln.today
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