If an X.509 certificate contains a malformed policy constraint and policy processing is enabled, then a write lock will be taken twice recursively. On some operating systems this results in a denial of service when the affected process hangs. Policy processing being enabled on a publicly facing server is not considered to be a common setup. Policy processing is enabled by passing the `-policy' argument to the command line utilities or by calling either `X509_VERIFY_PARAM_add0_policy' or `X509_VERIFY_PARAM_set1_policies' functions