Vulnerabilities

Vulnerability · CVE-2026-72897

Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake

Published Sep 29, 2026 · catalog updated Sep 29, 2026 · OpenSSL OpenSSL

Last checked Oct 27, 2026. A connected source was read within the last 7 days.

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No confirmed exploitation is on record for CVE-2026-72897. EPSS is 0.39%. Act only if a listed version of OpenSSL OpenSSL is installed.

Severity

High7.5

Known exploitation

Not in CISA/VulnCheck KEV

EPSS

0.39%

Remediation

Advisory link

Affected products

vendor OpenSSL OpenSSL

Issue summary: 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. Applications which never call SSL_set_SSL_CTX() are not affected. Impact summary: 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. This may lead to a Denial of Service. CWE: CWE-787: Out-of-bounds Write Description: A TLS connection records how many certificate slots it has when it is created, taken from the SSL_CTX that created it: the built-in certificate types plus one slot for each provider TLS-SIGALG entry that context was aware of. That count sizes an internal array of per-slot certificate validity flags. An application may replace a connection's SSL_CTX part way through the handshake by calling SSL_set_SSL_CTX(), most commonly from a servername callback in order to serve a different virtual host. Doing so did not refresh the recorded count. A provider signature algorithm's slot index is its position in the list of whichever context resolves it, so if the replacement context is aware of more of them than the original, an algorithm offered by the peer can resolve to an index beyond the end of the array. Processing the peer's signature algorithms then reads one four byte word past the end for each such algorithm and, where the word read is zero, writes a fixed value over it. A peer offering many of them can corrupt heap metadata and abort the process. Only provider signature algorithms which occupy one of the excess slots, and which the server also has configured, have this effect. Codepoints the replacement context does not recognise are discarded without being resolved to a slot, and provider signature algorithms are usable only from TLS 1.3. The two contexts mus