Due to use of a potentially dangerous function Squid and the
default certificate validation helper are vulnerable to a Denial
of Service attack when processing TLS certificates.

Severity:

This problem allows a trusted client to perform Denial of Service
when opening TLS connections with a server for HTTPS.

This problem allows a trusted client to perform Denial of Service
when opening TLS connections to a server for SSL-Bump intercepted
transactions.

This attack is limited to Squid built with OpenSSL features and
opening peer or server connections for HTTPS traffic and SSL-Bump
server handshakes.

CVSS Score of 8.3
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/E:F/RL:O/RC:C/CR:X/IR:X/AR:H/MAV:N/MAC:H/MPR:N/MUI:X/MS:C/MC:N/MI:N/MA:H&version=3.1

Updated Packages:

This bug is fixed by Squid versions 4.12 and 5.0.3.

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

Squid 4:

http://www.squid-cache.org/Versions/v4/SQUID-2020_6.patch

Squid 5:

http://www.squid-cache.org/Versions/v5/SQUID-2020_6.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-2.x up to and including 2.7.STABLE9 are not vulnerable.

All Squid-3.x up to and including 3.4.14 built without
--enable-openssl are not vulnerable.

All Squid-3.x up to and including 3.4.14 built with
--disable-openssl are not vulnerable.

All Squid-3.x up to and including 3.4.14 built with
--enable-openssl are vulnerable.

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

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

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

All Squid-4.x up to and including 4.11 built without
--with-openssl are not vulnerable.

All Squid-4.x up to and including 4.11 built with
--without-openssl are not vulnerable.

All Squid-4.x up to and including 4.11 built with --with-openssl
are vulnerable.

Squid-5.0.1 and 5.0.2 built without --with-openssl are not
vulnerable.

Squid-5.0.1 and 5.0.2 built with --without-openssl are not
vulnerable.

Squid-5.0.1 and 5.0.2 built with --with-openssl are vulnerable.

Workaround:

• For interception proxies using SSL-Bump functionality there is
  no workaround.

• For reverse-proxy the GnuTLS support available in Squid-4 may
  provide sufficient functionality. The vulnerable certificate
  validator helper feature is not supported yet by GnuTLS builds.

• Other installations just needing to relay HTTPS do not need
  OpenSSL support and should be able to run a build that does not
  have --with-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
http://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 Christof Gerber and Mario Galli of Open Systems AG.

Fixed by Christos Tsantilas of The Measurement Factory.

Revision history:

2020-03-04 09:31:23 UTC Initial Report
2020-05-15 04:54:54 UTC Patches Released

END