Applications parsing invalid CMS structures can crash with a NULL pointer dereference. This is caused by a bug in the handling of the ASN.1 CHOICE type in OpenSSL 1.1.0 which can result in a NULL value being passed to the structure callback if an attempt is made to free certain invalid encodings. Only CHOICE structures using a callback which do not handle NULL value are affected.
OpenSSL 1.1.0 users should upgrade to 1.1.0c
This issue does not affect OpenSSL versions prior to 1.1.0
This issue was reported to OpenSSL on 12th October 2016 by Tyler Nighswander of ForAllSecure. The fix was developed by Stephen Henson of the OpenSSL development team.