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CVE-2026-72897— Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake

Quick assessment

Affected
OpenSSL OpenSSL
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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

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I. Basic Information for CVE-2026-72897

Vulnerability Information

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Vulnerability Title
Out-of-Bounds Access After SSL_set_SSL_CTX() During a Handshake
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
OpenSSL OpenSSL 4.0.0 ~ 4.0.3 -

II. Public POCs for CVE-2026-72897

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III. Intelligence Information for CVE-2026-72897

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Other References for CVE-2026-72897 (5)

Same Patch Batch · OpenSSL · 2026-09-29 · 14 CVEs total

CVE-2026-35189 Excessive Memory Allocation in Relative CRLDP Processing
CVE-2026-35191 QUIC Unvalidated Amplification Credit may be Over Accounted
CVE-2026-75806 Unauthenticated and Undersized DTLS 1.2 AEAD Record Causes DoS
CVE-2026-75804 QUIC Connection-Level Flow Control is Not Enforced for Streams
CVE-2026-75805 NULL Pointer Dereference in CMP Client Revocation Response Handling
CVE-2026-42772 Potential CPU DoS via O(n^2) Fragment Reassembly in QUIC
CVE-2026-54873 QUIC STREAM Fragment Metadata DoS
CVE-2026-54872 Timing Side-Channel in Scalar Multiplication for Non-NIST EC Curves
CVE-2026-54875 Non-Constant-Time SM2 Scalar Multiplication on ARM64 and RISC-V
CVE-2026-77696 Timing Side-Channel in SM2 Signature Generation
CVE-2026-84782 DTLS Retransmits Handshake Messages From a Stale Buffer Offset
CVE-2026-84784 QUIC: Unbounded RETIRE_CONNECTION_ID Backlog
CVE-2026-84783 Use-After-Free in X.509 Extension Cache Under Concurrent Use

IV. Related Vulnerabilities

Same product: OpenSSL
Same vendor: OpenSSL
Same weakness: CWE-787

V. Comments for CVE-2026-72897

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