Tiny ASN.1 Library (libtasn1) before 0.2.18, as used by (1) GnuTLS 1.2.x before 1.2.10 and 1.3.x before 1.3.4, and (2) GNU Shishi, allows attackers to crash the DER decoder and possibly execute arbitrary code via "out-of-bounds access" caused by invalid input, as demonstrated by the ProtoVer SSL test suite.