The MITRE CVE dictionary describes this issue as:
Multiple memory leaks in tools/cachemgr.cc in cachemgr.cgi in Squid 2.x and 3.x before 3.1.22, 3.2.x before 3.2.4, and 3.3.x before 126.96.36.199 allow remote attackers to cause a denial of service (memory consumption) via (1) invalid Content-Length headers, (2) long POST requests, or (3) crafted authentication credentials.
Find out more about CVE-2012-5643 from the
MITRE CVE dictionary dictionary and
Red Hat Enterprise Linux 5 is now in Production 3 Phase of the support and maintenance life cycle. This has been rated as having Moderate security impact and is not currently planned to be addressed in future updates. For additional information, refer to the Red Hat Enterprise Linux Life Cycle: https://access.redhat.com/support/policy/updates/errata/.