CVE 2012-0021
The log_cookie function in mod_log_config.c in the mod_log_config module in the Apache HTTP Server 2.2.17 through 2.2.21, when a threaded MPM is used, does not properly handle a %{}C format string, which allows remote attackers to cause a denial of service (daemon crash) via a cookie that lacks both a name and a value.
See the 
CVE page on Mitre.org
for more details.
