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SQUID-2021:3 Denial of Service issue in Cache Manager

yadij published GHSA-m47m-9hvw-7447 May 10, 2021


squid (Squid)

Affected versions

1.0-4.14, 5.0-5.0.5

Patched versions

4.15, 5.0.6


Due to an incorrect parser validation bug Squid is vulnerable to
a Denial of Service attack against the Cache Manager API.


This problem allows a trusted client to trigger memory leaks
which over time lead to a Denial of Service against Squid and
the machine it is operating on.

This attack is limited to clients with Cache Manager API access

CVSS Score of 7.8

Updated Packages:

This bug is fixed by Squid versions 4.15 and 5.0.6.

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

Squid 4:

Squid 5:

If you are using a prepackaged version of Squid then please refer
to the package vendor for availability information on updated

Determining if your version is vulnerable:

Squid older than 3.5.28 have not been tested and should be
assumed to be vulnerable.

All Squid-4.x up to and including 4.14 are vulnerable.

All Squid-5.x up to and including 5.0.4 are vulnerable.



Disable Cache Manager access entirely if not needed.

Place the following line in squid.conf before lines containing
"allow" :

http_access deny manager


Harden Cache Manager access privileges.

For example; require authentication or other access controls in
http_access beyond the default IP address restriction.

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 mailing list is your
primary support point. For subscription details see

For reporting of non-security bugs in the latest STABLE release
the squid bugzilla database should be used

For reporting of security sensitive bugs send an email to the 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.


This vulnerability was discovered by Joshua Rogers of Opera

Fixed by Amos Jeffries of Treehouse Networks Ltd.

Revision history:

2021-03-03 17:02:25 UTC Initial Report
2021-03-16 01:59:45 UTC Patch Released
2021-03-17 06:19:09 UTC CVE Assignment




CVSS Score

6.8 Moderate