CVE-2026-84784

OpenSSL 4.0 contains a use-after-free vulnerability (CWE-416) in the caching of X.509 certificate extensions. When several threads concurrently use the same certificate for the first time, one thread may free the cached extension data while another thread is still using it. This can crash the process, resulting in a Denial of Service.

The DTLS retransmission logic incorrectly handles a handshake message write that is suspended part-way through. The retransmitted message can be read past the message buffer, disclosing heap memory or causing a crash and Denial of Service.

SM2 signature generation uses non-constant-time arithmetic on secret values, forming a timing side-channel. An attacker able to measure SM2 signing times may learn information about the per-signature secret nonce, which over many signatures can lead to recovery of the private key. Applications performing SM2 signature generation are affected on all platforms.

An established DTLS 1.2 association using an AEAD cipher suite can be terminated by a single unauthenticated datagram whose encrypted fragment is shorter than the mandatory explicit IV and authentication tag overhead. The record layer passes the record length to the cipher before checking it is long enough, causing an internal error instead of treating the record as failed authentication.

A NULL pointer dereference vulnerability in the OpenSSL CMP client. When a client requests certificate revocation based on a PKCS#10 CSR and the server returns a specially crafted certificate name in its response, the client reads from a NULL pointer and crashes. Only clients that identify the certificate via CSR (e.g. 'openssl cmp -cmd rr -csr' or OSSL_CMP_exec_RR_ses() with OSSL_CMP_CTX_set1_p10CSR()) are affected.

The OpenSSL QUIC stack does not enforce connection-level flow control for streams. A malicious remote peer can send more bytes as long as they fit within stream flow control limits, leading to excessive memory allocation.

A TLS server that calls SSL_set_SSL_CTX() to switch a connection to a different SSL_CTX part way through a handshake may access memory beyond the end of an internal array if the replacement context knows about more provider signature algorithms than the context the connection was created from. A remote peer may be able to cause a small out-of-bounds read, and in some circumstances a fixed-value out-of-bounds write, on the server heap, potentially leading to a Denial of Service.

OpenSSL's optimized scalar point multiplication implementation for SM2 private key operations on ARM64 and RISC-V platforms is not constant-time. Conditional branches and table lookups depend on the bits of the secret scalar, so execution time and cache-access patterns leak information about the private key or signature nonce.

A vulnerability in the QUIC implementation in OpenSSL allows a remote attacker to keep allocated packet buffer memory for an extended period by sending specially crafted packets. The issue stems from missing resource allocation limits (CWE-770), potentially leading to excessive memory consumption.

The generic elliptic-curve scalar multiplication used for ECDSA and SM2 signature operations with curves lacking a dedicated implementation leaks information about the secret nonce through timing. An attacker measuring signing times may learn the nonce, which over many signatures can lead to private key recovery.