[squid-announce] [ADVISORY] SQUID-2025:2 Information Disclosure in Error handling.

[Amos Jeffries]

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     Squid Proxy Cache Security Update Advisory SQUID-2025:2
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Advisory ID:       | SQUID-2025:2
Date:              | Oct 15, 2025
Summary:           | Information Disclosure in Error 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 -> 7.1
Fixed in version:  | Squid 7.2
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Problem Description:

  Due to a failure to redact HTTP Authentication credentials
  Squid is vulnerable to an Information Disclosure attack.

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Severity:

  This problem allows a script to bypass Browser security
  protections and learn the credentials a trusted client uses to
  authenticate.

  This problem potentially allows a remote client to identify
  security tokens or credentials used internally by a web
  application using Squid for backend load balancing.

  These attacks do not require Squid to be configured with HTTP
  Authentication.

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Updated Packages:

  This bug is fixed by Squid version 7.2.

  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/0951a0681011dfca3d78c84fd7f1e19c78a4443f>

  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:

  The following test can be used to determine if your Squid has
  a vulnerable configuration:

     squid -k parse 2>&1 | grep "email_err_data"

  All Squid with `email_err_data off` are not vulnerable.

  All Squid up to and including 7.1 with `email_err_data on`
  are vulnerable.

  All Squid up to and including 7.1 without `email_err_data`
  are vulnerable.

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Workaround:

  Disable debug information in administrator mailto links
  generated by Squid. By configuring squid.conf with:

     email_err_data off

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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
  <http://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 by Leonardo Giovannini of
  Doyensec.

  Fixed by Amos Jeffries of Treehouse Networks Ltd.

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Revision history:

  2025-09-12 08:52:20 UTC Initial Report
  2025-10-11 07:42:00 UTC Patch Released
  2025-10-13 14:35:00 UTC CVE Assignment
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END