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Squid Proxy Cache Security Update Advisory SQUID-2026:2
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Advisory ID: | SQUID-2026:2 (CVE-2026-32748)
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
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Problem Description:
Due to premature release of resource during expected lifetime and
heap Use-After-Free bugs, Squid is vulnerable to Denial of
Service when handling ICP traffic.
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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.
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Updated Packages
This bug is 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/703e07d25ca6fa11f52d20bf0bb879e22ab7481b>
If you are using a prepackaged version of Squid then please
refer to the package vendor for availability information on
updated packages.
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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.
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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.
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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.
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Credits
Discovered and Fixed by Alex Rousskov, The Measurement Factory
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Revision history:
2026-02-08 21:20:00 EDT Report of vulnerability
2026-02-18 21:13:26 UTC official fixes in master branch
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