# CVE-2026-72897: Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake CVE-2026-72897 is fixed in 18 products on 1 platform, first by libssl3t64 3.5.5-1ubuntu3.6, released September 28, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-72897 - Priority: High - CVSS: 7.5 (Important) - EPSS: 0.0039 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Sep 28, 2026 - Weakness: Out-of-bounds Write - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-72897 ## Description 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 must therefore be aware of different numbers of provider signature algorithms, which requires separate library contexts, a provider loaded between the two being created, or providers which differ in what they advertise - in 4.0, for example, the default provider advertises SM2 where the FIPS provider does not. A deployment meeting the condition is also unable to negotiate the affected algorithms with legitimate clients, since the same stale count hides the corresponding certificates, so the misconfiguration is likely to be noticed. For that reason, and because the configuration is not the default, this issue has been assessed as Low severity. FIPS impact: no No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | edk2-aarch64 amzn 2023 | 20260508-2.amzn2023 | [ALAS2023-2026-3227](https://patchblox.com/security/data/fix/linux/alas2023-2026-3227.md) | Nov 7, 2026 | | Linux | edk2-ovmf amzn 2023 | 20260508-2.amzn2023 | [ALAS2023-2026-3227](https://patchblox.com/security/data/fix/linux/alas2023-2026-3227.md) | Nov 7, 2026 | | Linux | edk2-shell-aa64 amzn 2023 | 20260508-2.amzn2023 | [ALAS2023-2026-3227](https://patchblox.com/security/data/fix/linux/alas2023-2026-3227.md) | Nov 7, 2026 | | Linux | edk2-shell-x64 amzn 2023 | 20260508-2.amzn2023 | [ALAS2023-2026-3227](https://patchblox.com/security/data/fix/linux/alas2023-2026-3227.md) | Nov 7, 2026 | | Linux | libssl3t64 Ubuntu 26.04.1 LTS (resolute) | 3.5.5-1ubuntu3.6 | [libssl3t64 3.5.5-1ubuntu3.6](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-libssl3t64-3.5.5-1ubuntu3.6.md) | Sep 28, 2026 | | Linux | openssl Debian 13.5 (trixie) | 3.5.7-1~deb13u3 | [DEBIAN-CVE-2026-72897](https://patchblox.com/security/data/fix/linux/debian-cve-2026-72897.md) | Sep 30, 2026 | | Linux | openssl Debian 14 | 3.6.5-1 | [DEBIAN-CVE-2026-72897](https://patchblox.com/security/data/fix/linux/debian-cve-2026-72897.md) | Sep 30, 2026 | | Linux | openssl Ubuntu 26.04.1 LTS (resolute) | 3.5.5-1ubuntu3.6 | [openssl 3.5.5-1ubuntu3.6](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-openssl-3.5.5-1ubuntu3.6.md) | Sep 28, 2026 | | Linux | openssl amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-3 opensuse-leap 16.0 | 3.5.0-160000.11.1 | [OPENSUSE-SU-2026:22102-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-22102-1.md) | Nov 7, 2026 | | Linux | openssl-3 sles 15.7 | 3.5.0-150700.5.53.2 | [SUSE-SU-2026:4414-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-4414-1.md) | Oct 2, 2026 | | Linux | openssl-3 sles 16.0 | 3.5.0-160000.11.1 | [SUSE-SU-2026:24245-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-24245-1.md) | Nov 7, 2026 | | Linux | openssl-debuginfo amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-debugsource amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-devel amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-fips-provider-latest amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-fips-provider-latest-debuginfo amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-libs amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-libs-debuginfo amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-perl amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-provider-legacy Ubuntu 26.04.1 LTS (resolute) | 3.5.5-1ubuntu3.6 | [openssl-provider-legacy 3.5.5-1ubuntu3.6](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-openssl-provider-legacy-3.5.5-1ubuntu3.6.md) | Sep 28, 2026 | | Linux | openssl-snapsafe-libs amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | | Linux | openssl-snapsafe-libs-debuginfo amzn 2023 | 1:3.5.8-1.amzn2023.0.3 | [ALAS2023-2026-3204](https://patchblox.com/security/data/fix/linux/alas2023-2026-3204.md) | Nov 7, 2026 | --- Data as of 2026-11-09T13:31:49Z UTC. 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