The get_repeat_type function in basic_regex_creator.hpp in the Boost regex library (aka Boost.Regex) in Boost 1.33 and 1.34 allows context-dependent attackers to cause a denial of service (NULL dereference and crash) via an invalid regular expression.

More... (http://nvd.nist.gov/nvd.cfm?cvename=CVE-2008-0172)