An OpenSSL TLS server may crash if sent a maliciously crafted renegotiation ClientHello message from a client. If a TLSv1.2 renegotiation ClientHello omits the signature_algorithms extension (where it was present in the initial ClientHello), but includes a signature_algorithms_cert extension then a NULL pointer dereference will result, leading to a crash and a denial of service attack. A server is only vulnerable if it has TLSv1.2 and renegotiation enabled (which is the default configuration). OpenSSL TLS clients are not impacted by this issue. All OpenSSL 1.1.1 versions are affected by this issue. Users of these versions should upgrade to OpenSSL 1.1.1k. OpenSSL 1.0.2 is not impacted by this issue. Fixed in OpenSSL 1.1.1k (Affected 1.1.1-1.1.1j).

IBM GSKit 7.x before 7.0.4.48 and 8.x before 8.0.50.16, as used in IBM Security Directory Server (ISDS) and Tivoli Directory Server (TDS), allows remote attackers to cause a denial of service (application crash or hang) via a malformed X.509 certificate chain.

IBM Global Security Kit (aka GSKit), as used in Content Manager OnDemand 8.5 and 9.0 and other products, allows remote attackers to cause a denial of service via a crafted handshake during resumption of an SSLv2 session.