The (1) asn1_read_value_type and (2) asn1_read_value functions in GNU Libtasn1 before 3.6 allows context-dependent attackers to cause a denial of service (NULL pointer dereference and crash) via a NULL value in an ivalue argument.
lib/x509/verify.c in GnuTLS before 3.1.21 and 3.2.x before 3.2.11 treats version 1 X.509 certificates as intermediate CAs, which allows remote attackers to bypass intended restrictions by leveraging a X.509 V1 certificate from a trusted CA to issue new certificates.
lib/x509/verify.c in GnuTLS before 3.1.22 and 3.2.x before 3.2.12 does not properly handle unspecified errors when verifying X.509 certificates from SSL servers, which allows man-in-the-middle attackers to spoof servers via a crafted certificate.
Mutt 1.5.19, when linked against (1) OpenSSL (mutt_ssl.c) or (2) GnuTLS (mutt_ssl_gnutls.c), allows connections when only one TLS certificate in the chain is accepted instead of verifying the entire chain, which allows remote attackers to spoof trusted servers via a man-in-the-middle attack.