Due to an Improper Validation of Specified Index
bug Squid is vulnerable to a Denial of Service
attack against SSL Certificate validation.

Severity:

This problem allows a remote server to perform Denial of
Service against Squid Proxy by initiating a TLS Handshake with
a specially crafted SSL Certificate in a server certificate
chain.

This attack is limited to HTTPS and SSL-Bump.

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_4.patch

Squid 6:

http://www.squid-cache.org/Versions/v6/SQUID-2023_4.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:

All Squid older than 3.3.0.1 are not vulnerable.

All Squid-3.3 up to and including 3.4.14 compiled without
--enable-ssl are not vulnerable.

All Squid-3.3 up to and including 3.4.14 compiled using
--enable-ssl are vulnerable.

All Squid-3.5 up to and including 3.5.28 compiled without
--with-openssl are not vulnerable.

All Squid-3.5 up to and including 3.5.28 compiled using
--with-openssl are vulnerable.

All Squid-4.x up to and including 4.16 compiled without
--with-openssl are not vulnerable.

All Squid-4.x up to and including 4.16 compiled using
--with-openssl are vulnerable.

Squid-5.x up to and including 5.9 compiled without
--with-openssl are not vulnerable.

All Squid-5.x up to and including 5.9 compiled using
--with-openssl are vulnerable.

All Squid-6.x up to and including 6.3 compiled without
--with-openssl are not vulnerable.

All Squid-6.x up to and including 6.3 compiled using
--with-openssl are vulnerable.

Workaround:

Either,

Disable use of SSL-Bump features:

• Remove all ssl-bump options from http_port and https_port
• Remove all ssl_bump directives from squid.conf

Or,

Rebuild Squid using --without-openssl.

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 Andreas Weigel

Revision history:

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

END