Heap-based buffer overflow in a regular-expression parser in Mozilla Network Security Services (NSS) before 3.12.3 as used in Firefox Thunderbird SeaMonkey Evolution Pidgin and AOL Instant Messenger (AIM) allows remote SSL servers to cause a denial of service (application crash) or possibly execute arbitrary code via a long domain name in the subject's Common Name (CN) field of an X.509 certificate related to the cert_TestHostName function.