__________________________________________________________________
Squid Proxy Cache Security Update Advisory SQUID-2026:1
__________________________________________________________________
Advisory ID: | SQUID-2026:1 (CVE-2026-33526)
Date: | March 25, 2026
Summary: | Denial of Service in ICP Request handling
Affected versions: | Squid 3.x -> 3.5.28
| Squid 4.x -> 4.17
| Squid 5.x -> 5.9
| Squid 6.x -> 6.14
| Squid 7.x -> 7.4
Fixed in version: | Squid 7.5
__________________________________________________________________
Problem Description:
Due to a heap Use-After-Free bug Squid is vulnerable to Denial
of Service when handling ICP traffic.
__________________________________________________________________
Severity:
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.
__________________________________________________________________
Updated Packages
These bugs were fixed in Squid version 7.5.
In addition, patches addressing this problem for the stable
releases can be found in our patch archives:
Squid 7:
<https://github.com/squid-cache/squid/commit/8a7d42f9d44befb8fcbbb619505587c8de6a1e91>
If you are using a prepackaged version of Squid then please
refer to the package vendor for availability information on
updated packages.
__________________________________________________________________
Determining if your version is vulnerable
Run the following command to identify whether your Squid
has been configured with ICP enabled:
squid -k parse 2>&1 | grep -E "(icp|udp)_port" | tail -n1
All Squid configured with port 0 are not vulnerable.
All Squid-3.0 up to and including 7.4 configured with
a non-zero port should be assumed to be vulnerable.
All Squid-3.2 up to and including 7.4 configured without
any port value can be assumed to be not vulnerable.
__________________________________________________________________
Workaround
Either,
* Do not enable ICP support,
Or,
* explicitly disable ICP using "icp_port 0".
Warning: These problems _cannot_ be mitigated by denying ICP
queries using icp_access rules.
__________________________________________________________________
Contact details for the Squid project:
For installation / upgrade support on binary packaged versions
of Squid: Your first point of contact should be your binary
package vendor.
If you install and build Squid from the original Squid sources
then the <[email protected]> mailing list is
your primary support point. For subscription details see
<https://www.squid-cache.org/Support/mailing-lists.html>.
For reporting of non-security bugs in the latest STABLE release
the squid bugzilla database should be used
<https://bugs.squid-cache.org/>.
For reporting of security sensitive bugs send an email to the
<[email protected]> mailing list. It's a closed
list (though anyone can post) and security related bug reports
are treated in confidence until the impact has been established.
__________________________________________________________________
Credits
Discovered by:
* Joshua Rogers with ZeroPath
* Asim Viladi Oglu Manizada
Fixed by:
* Joshua Rogers with ZeroPath
__________________________________________________________________
Revision history:
2025-09-07 20:22:00 EDT Report of the first set of vulnerabilities
2026-01-26 08:48:00 EDT Report of additional vulnerabilities
2026-02-10 19:58:49 UTC official fixes in master branch
__________________________________________________________________
END
