[USN-5771-1] Squid regression

USN-3557-1 fixed vulnerabilities in Squid. This update introduced a regression
which could cause the cache log to be filled with many Vary loop messages. This
update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Mathias Fischer discovered that Squid incorrectly handled certain long
strings in headers. A malicious remote server could possibly cause Squid to
crash, resulting in a denial of service. This issue was only addressed in
Ubuntu 16.04 LTS. (CVE-2016-2569)

William Lima discovered that Squid incorrectly handled XML parsing when
processing Edge Side Includes (ESI). A malicious remote server could
possibly cause Squid to crash, resulting in a denial of service. This issue
was only addressed in Ubuntu 16.04 LTS. (CVE-2016-2570)

Alex Rousskov discovered that Squid incorrectly handled response-parsing
failures. A malicious remote server could possibly cause Squid to crash,
resulting in a denial of service. This issue only applied to Ubuntu 16.04
LTS. (CVE-2016-2571)

Santiago Ruano Rincón discovered that Squid incorrectly handled certain
Vary headers. A remote attacker could possibly use this issue to cause
Squid to crash, resulting in a denial of service. This issue was only
addressed in Ubuntu 16.04 LTS. (CVE-2016-3948)

Louis Dion-Marcil discovered that Squid incorrectly handled certain Edge
Side Includes (ESI) responses. A malicious remote server could possibly
cause Squid to crash, resulting in a denial of service. (CVE-2018-1000024)

Louis Dion-Marcil discovered that Squid incorrectly handled certain Edge
Side Includes (ESI) responses. A malicious remote server could possibly
cause Squid to crash, resulting in a denial of service. (CVE-2018-1000027)