OpenSSL Security Advisory [29th September 2026]

OpenSSL’s DTLS retransmission logic mishandles a handshake message write that is suspended part-way through, which is an out-of-bounds read (CWE-125). If the underlying transport returns WANT_WRITE mid-message and the retransmission timer then fires, the resend reuses the suspended write’s buffer and position, so the message body can be leftover bytes from a larger in-flight message and can be read past the allocated buffer. A DTLS peer can receive that leftover heap memory as plaintext handshake data, or the process can crash and cause a denial of service if the read hits unmapped memory; separately, completing a retransmission while a write is suspended corrupts shared bookkeeping and can abort the process in a debugging build when SSL_read, SSL_write, SSL_accept, or SSL_connect later resumes the write. Applications and devices that use OpenSSL for DTLS handshakes are affected; the issue is outside the FIPS module boundary. There is no known public proof of concept and the CVE is not listed in CISA KEV.