Problem Description:

Due to incorrect data validation Squid is vulnerable to HTTP Request Smuggling
attacks against HTTP and HTTPS traffic. This leads to cache poisoning.

Severity:

This problem is serious because it allows any client, including
browser scripts, to bypass local security and poison the proxy
cache and any downstream caches with content from an arbitrary
source.

CVSS Score of 9.3
https://nvd.nist.gov/vuln-metrics/cvss/v3-calculator?vector=AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N/E:F/RL:O/RC:C/CR:H/IR:H/AR:X/MAV:N/MAC:L/MPR:L/MUI:N/MS:C/MC:H/MI:H/MA:N&version=3.1

Updated Packages:

This bug is fixed by Squid versions 4.13 and 5.0.4.

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_10.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 with relaxed_header_parser configured "off" are not vulnerable.

All Squid-3.x up to and including 3.5.28 with relaxed_header_parser configured to
"on" or "warn" are vulnerable.

All Squid-3.x up to and including 3.5.28 without relaxed_header_parser configured
are vulnerable.

All Squid-4.x up to and including 4.12 with relaxed_header_parser configured to
"on" or "warn" are vulnerable.

All Squid-4.x up to and including 4.12 without relaxed_header_parser configured
are vulnerable.

All Squid-5.x up to and including 5.0.3 with relaxed_header_parser configured to
"on" or "warn" are vulnerable.

All Squid-5.x up to and including 5.0.3 without relaxed_header_parser configured
are vulnerable.

Workaround:

Disable the relaxed HTTP parser in squid.conf:

relaxed_header_parser off

Note, traffic which does not correctly obey HTTP specifications
will be rejected instead of converted to standards compliance.

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 Amit Klein of Safebreach.

Fixed by Amos Jeffries of Treehouse Networks Ltd.

Revision history:

2020-05-11 08:21:58 UTC Initial Report
2020-07-17 17:11:50 UTC CVE Allocated