Due to an Incorrect Conversion between Numeric Types
bug Squid is vulnerable to a Denial of Service
attack against FTP Native Relay input validation.

Due to an Incorrect Conversion between Numeric Types
bug Squid is vulnerable to a Denial of Service
attack against ftp:// URL validation and access control.

Severity:

This problem allows a remote client to perform Denial of Service
when sending ftp:// URLs in HTTP Request messages or constructing
ftp:// URLs from FTP Native input.

This issue is triggered during access control security checks,
meaning clients may not have been permitted to use the proxy yet.

FTP support is always enabled and cannot be disabled completely.

CVSS Score of 8.6
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H&version=3.1

Updated Packages:

This bug is fixed by Squid version 6.4.

In addition, patches addressing this problem for the stable
releases can be found in our patch archives:

Squid 5:

http://www.squid-cache.org/Versions/v5/SQUID-2023_5.patch

Squid 6:

http://www.squid-cache.org/Versions/v6/SQUID-2023_5.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 5.0.3 are not vulnerable.

All Squid-5.0.4 up to and including 5.6 are vulnerable.

All Squid-6.x up to and including 6.3 are vulnerable.

Workaround:

• The FTP Native Relay input validation vector can be secured by
  removing all ftp_port directives from squid.conf.

• There are no workarounds to avoid the ftp:// URL validation and
  access control vector.

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@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@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 by Joshua Rogers of Opera
Software.

Fixed by The Measurement Factory.

Revision history:

2023-10-12 11:53:02 UTC Initial Report

END