# CVE-2026-72897: OpenSSL out-of-bounds read/write in SSL_set_SSL_CTX

Source: https://junglewise.ai/threats/cve-2026-72897-issue-summary-a-tls-server-that-calls-ssl-set-ssl-ctx-to-switch-a  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-29  
License: CC BY 4.0 with a link back

CVE-2026-72897 · Severity: info · Published 2026-09-29

OpenSSL, a cryptographic library used to secure internet communications, contains a flaw in how it handles TLS connections when switching to a different security context mid-handshake. An attacker connecting to a vulnerable server could trigger a small out-of-bounds memory read or write, potentially causing the server to crash and denying service to legitimate users. This only affects servers that use specific advanced configuration options and is not a default vulnerability.

Technologies: [OpenSSL](https://junglewise.ai/threats/technologies/openssl). Vendors: [OpenSSL](https://junglewise.ai/threats/vendors/openssl).

## Quick answers

**Is CVE-2026-72897 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-72897 being exploited in the wild.

**How severe is CVE-2026-72897?** Informational severity, published 29 September 2026.

**Which products and versions are affected?** OpenSSL OpenSSL.

**Is there a fix for CVE-2026-72897?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-72897 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-72897?** Check whether you run OpenSSL. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A TLS server using SSL_set_SSL_CTX() to switch SSL contexts during the handshake (common in SNI callbacks for multi-host setups) fails to update its internal array size when the new context supports more provider signature algorithms. When a peer offers signature algorithms beyond the stale array bounds, the code reads and conditionally writes to out-of-bounds heap memory, potentially corrupting heap metadata. The vulnerability requires TLS 1.3, different provider signature algorithm counts between contexts, and misconfigured certificate slots that would already prevent legitimate negotiation.

## Affected products

- OpenSSL OpenSSL

## Timeline

- 2026-09-29: disclosed

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