Due to a Use-After-Free bug Squid is vulnerable to a Denial of
Service attack against collapsed forwarding

Severity:
This problem allows a remote client to perform Denial of
Service attack on demand when Squid is configured with collapsed
forwarding.

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 6.0.1.
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:
Run the following command to identify how (and whether)
your Squid has been configured with collapsed forwarding:

`squid -k parse 2>&1 | grep collapsed_forwarding`
All Squid-3.5 up to and including 5.9 configured with
"collapsed_forwarding on" are vulnerable.

All Squid-3.5 up to and including 5.9 configured with
"collapsed_forwarding off" are not vulnerable.

All Squid-3.5 up to and including 5.9 configured without any
"collapsed_forwarding" directive are not vulnerable.

Workaround:
Remove all collapsed_forwarding lines from your squid.conf.

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.

References:
https://github.com/squid-cache/squid/security/advisories/GHSA-rj5h-46j6-q2g5
https://megamansec.github.io/Squid-Security-Audit/trace-uaf.html