[squid-announce] [ADVISORY] SQUID-2026:8 Stack Buffer Overflow in ICAP Authentication

[Amos Jeffries]

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     Squid Proxy Cache Security Update Advisory SQUID-2026:8
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  Advisory ID:       | SQUID-2026:8
  Date:              | 2026-08-25
  Summary:           | Stack Buffer Overflow in ICAP Authentication
  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 -> 7.6
  Fixed in version:  | Squid 7.7
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Problem Description:

  Due to an Improper Input Validation (CWE-20) bug
  Squid is vulnerable to a Stack-based Buffer Overflow (CWE-121)
  when configured to use an ICAP Server in conjunction with a
  misbehaving external ACL authentication helper.

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Severity:

  This problem allows an external acl helper to perform an
  out-of-bounds write when passing credentials as user= and
  password= annotations for use by an ICAP Service.

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Updated Packages:

  This bug is fixed by Squid version 7.7

  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/8b3c2f2eea22886288edb47d4c30177bf8673650.patch>

  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:

  Squid older than 3.5.28 have not been tested but should be
  considered vulnerable.

  All Squid-4.x up to and including 4.17 are not vulnerable.

  All Squid-5.x up to and including 5.9 are vulnerable.

  All Squid-6.x up to and including 6.14 are vulnerable.

  All Squid-7.x up to and including 7.6 are vulnerable.

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Workaround:

  If vulnerable external ACL programs get credentials from Squid
  transactions, exclude vulnerable external ACLs from seeing
  transactions that contain excessively long credentials.

  Wrap vulnerable external ACL helper programs into an output
  filtering program to prevent excessively long credentials from
  reaching Squid.

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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 <squid-users at lists.squid-cache.org> 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
  <squid-bugs at lists.squid-cache.org> 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:

  This vulnerability was discovered independently by:
  breakingbad6, Yingpei Zeng and Yanzhao Shen,
  and Hcamael

  Fixed by Francesco Chemolli <<kinkie at squid-cache.org>>

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Revision history:

  2026-05-09 18:29:00 UTC Initial report
  2026-06-23 07:00:00 UTC Patch published
  2026-08-25 21:00:00 UTC Advisory drafted

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