CVE-2026-94419
Received Received - Intake

Session Cache Poisoning in wolfSSL

Publication date: 2026-09-27

Last updated on: 2026-09-27

Assigner: wolfSSL Inc.

Description
Without NO_SESSION_CACHE_REF, wolfSSL_get_session() does not return a session object but a ClientSession reference of the form {row, index, hash(sessionID)} into the process-global SessionCache, and ClientSessionToSession() validates it against that hash alone. Because the TLS 1.2 session ID is chosen by the server and sent in clear, AddSessionToCache() matches any other server's session on the same ID and overwrites the client-side entry with that server's master secret, cipher suite and version, while the handle continues to resolve; nothing on the write path compares the peer, the application's server ID or the WOLFSSL_CTX. Resuming through the handle then produces an abbreviated handshake in which no Certificate message is sent, so neither chain verification nor wolfSSL_check_domain_name() runs, and the attacker is accepted as the original server for the whole of that connection. Affected builds are those leaving NO_SESSION_CACHE_REF, NO_SESSION_CACHE, NO_CLIENT_CACHE and TITAN_SESSION_CACHE all undefined, which includes a plain ./configure, --enable-opensslextra and --enable-opensslall; fifteen integration options define NO_SESSION_CACHE_REF and are therefore not affected, among them --enable-all, --enable-distro, --enable-curl, --enable-nginx, --enable-haproxy, --enable-stunnel, --enable-wpas and the rest of the OPENSSL_COMPATIBLE_DEFAULTS family, and --enable-leanpsk, --enable-leantls, --enable-lowresource and --enable-tinytls13 disable the cache outright. The application must use the legacy reference flow, wolfSSL_get_session() or SSL_get_session() followed by wolfSSL_set_session(); wolfSSL_get1_session() returns the session object itself and is not affected, nor are wolfSSL_SetServerID() lookups. Only TLS 1.2 and below and DTLS 1.2 and below are reachable, since TLS 1.3 and ticket resumption with an empty ServerHello session ID both use a client-chosen cache key. The poisoned entry lives in the process-global cache, so it crosses WOLFSSL_CTX boundaries and persists until the entry is evicted or the session times out, 500 seconds by default. Releases v5.3.0 through v5.9.2 are affected; the fix adds a per-write generation counter to the cache and raises WOLFSSL_CACHE_VERSION from 2 to 3, so a cache persisted by an older build is rejected by a fixed one.

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Meta Information

Published
2026-09-27
Last Modified
2026-09-27
Generated
2026-09-27
AI Q&A
2026-09-27
EPSS Evaluated
N/A
NVD
CVE-2026-94419
EUVD
EUVD-2026-87906

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
wolfssl wolfssl 5.3.0
wolfssl wolfssl From 5.3.0 (inc) to 5.9.2 (inc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-287 When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

Attack-Flow Graph

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Executive Summary

This vulnerability in wolfSSL allows an attacker to impersonate a server during TLS session resumption. When certain configuration options are used, the session cache can be poisoned by overwriting a client's session entry with an attacker's session details. This bypasses certificate verification, allowing the attacker to be accepted as the original server without proper validation.

Impact Analysis

An attacker could intercept or manipulate encrypted traffic between a client and server by exploiting this flaw. This could lead to data breaches, unauthorized access to sensitive information, or man-in-the-middle attacks. The impact depends on the application's use of TLS session resumption and whether it relies on the vulnerable wolfSSL configurations.

Compliance Impact

This vulnerability could undermine compliance with GDPR, HIPAA, and other regulations requiring secure data transmission and authentication. By allowing unauthorized server impersonation, it may violate requirements for secure communication channels, data integrity, and proper identity verification.

Mitigation Strategies

Update wolfSSL to a version beyond v5.9.2 where the session cache generation counter fix is implemented. Ensure builds use configurations that define NO_SESSION_CACHE_REF or disable the cache outright, such as --enable-all or --enable-leantls.

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