[squid-announce] [ADVISORY] SQUID-2026:4 Memory disclosure in FTP gateway

[Amos Jeffries]

__________________________________________________________________

     Squid Proxy Cache Security Update Advisory SQUID-2026:4
__________________________________________________________________

Advisory ID:       | SQUID-2026:4 (CVE-2026-47729)
Date:              | 2026-06-14
Summary:           | Memory disclosure in FTP gateway
Affected versions: | Squid 3.x -> 3.5.27
                    | Squid 4.x -> 4.17
                    | Squid 5.x -> 5.9
                    | Squid 6.x -> 6.14
                    | Squid 7.x -> 7.5
Fixed in version:  | 7.6
__________________________________________________________________

Problem Description:

  Due to a  Improper Validation of Syntactic Correctness of Input
  bug, Squid is vulnerable to a Out-of-bounds Read
  attack against the FTP gateway.

__________________________________________________________________

Severity:

  This problem allows a trusted client to perform an Out-of-Bounds
  Read from random unrelated transactions when accessing a
  misbehaving FTP server through Squid's gateway feature.

__________________________________________________________________

Updated Packages:

This bug is fixed by Squid version 7.6

  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/865a131c7d557e68c965043d98c2eccae26deef8.patch>

  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:

  Squid older than 3.5.28 have not been tested and should be
  assumed to be vulnerable.

  All Squid-4.x are vulnerable.

  All Squid-5.x are vulnerable.

  All Squid-6.x are vulnerable.

  All Squid-7.x up to and including 7.5 are vulnerable.

__________________________________________________________________

Workaround:

  Place these squid.conf settings above any custom
  'http_access allow' lines in your squid.conf:

   acl FTP proto FTP
   acl ftp_allowlist url_regex ^ftp://trusted\.server\.example\.com

   http_access deny FTP !ftp_allowlist

  Note: The ftp_allowlist ACL is optional, for those who need to
        allow some FTP access to trusted servers. Best workaround
        is not to use one unless necessary.

__________________________________________________________________

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.

__________________________________________________________________

Credits:

This vulnerability was discovered and reported independently by
  Pavel Kohout of Aisle Research, and
  Lam Jun Rong of Calif.io in collaboration with Anthropic Research, and
  Youssef Awad of CTF.ae

Fixed by Alex Rousskov, The Measurement Factory.
__________________________________________________________________

Revision history:

  2026-03-04 12:41:54 UTC Initial Report by Pavel Kohout of Aisle Research
  2026-04-17: Initial Report by Lam Jun Rong
  2026-05-07: Initial Report by Youssef Awad
  2026-05-17 06:04:47 UTC patch published

__________________________________________________________________
END