EUVD-2026-39554
GHSA-w9rp-wwm2-fwmr
Severity by source
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attacker controls the server so AV:N and PR:N; non-default PQC hybrid build and client-initiated connection required so AC:H and UI:R; only client availability impacted at low severity.
Primary rating from Vendor (wolfssl).
CVSS VectorVendor: wolfssl
Lifecycle Timeline
2DescriptionCVE.org
Use-after-free in PQC hybrid key-share handling. This is an incomplete-fix follow-up to CVE-2026-5460 (released in 5.9.1): a malicious TLS 1.3 server sending a truncated PQC hybrid KeyShare can still trigger the error cleanup path to operate on freed memory.
AnalysisAI
Use-after-free in wolfSSL's TLS 1.3 PQC hybrid KeyShare processing exposes clients built with post-quantum hybrid support to a crash or memory corruption when connecting to a malicious server. This is a bypass of the incomplete fix for CVE-2026-5460 shipped in 5.9.1 - the pointer alias between keyShareEntry->key and ecc_kse->key in TLSX_KeyShare_ProcessPqcHybridClient is not re-synchronized after the inner ECC processing function frees its copy, leaving a dangling pointer that TLSX_KeyShare_FreeAll later passes to wc_ecc_free and XFREE. No public exploit or CISA KEV listing exists; the CVSS 4.0 score of 2.3 reflects limited real-world impact due to high attack complexity and non-default build requirements.
Technical ContextAI
wolfSSL is a lightweight, embedded TLS/SSL library widely used in IoT, automotive, and FIDO2 contexts. The affected function is TLSX_KeyShare_ProcessPqcHybridClient in src/tls.c, which handles TLS 1.3 key exchange for PQC hybrid groups - specifically SECP256R1MLKEM768, combining ECDH over SECP256R1 with ML-KEM-768 (formerly Kyber). CWE-416 (Use-After-Free) is the root cause: the inner function ProcessEcc_ex aliases ecc_kse->key to keyShareEntry->key, then unconditionally frees and NULLs ecc_kse->key during its error-path cleanup (triggered when wc_ecc_import_x963 rejects an invalid X9.63 point marker such as 0x05). The outer keyShareEntry->key retains the now-freed pointer. When wolfSSL_free subsequently invokes TLSX_KeyShare_FreeAll, wc_ecc_free and XFREE are called on that stale pointer, producing a use-after-free and double-free detectable by ASAN. The fix in PR #10327 re-syncs keyShareEntry->key = ecc_kse->key after the inner call returns, correctly inheriting whatever cleanup state the inner function left in ecc_kse->key (NULL on cleanup, live pointer on early exit).
RemediationAI
Apply the upstream fix from GitHub PR #10327 (https://github.com/wolfSSL/wolfssl/pull/10327) once a tagged release incorporating it becomes available; a specific patched release version is not confirmed in the available data - monitor https://www.wolfssl.com/docs/security-vulnerabilities/ for an official release announcement. As an immediate compensating control, rebuild wolfSSL without PQC hybrid support by omitting WOLFSSL_PQC_HYBRIDS and WOLFSSL_HAVE_MLKEM build flags; this eliminates the vulnerable code path entirely but removes post-quantum key exchange capability, which may conflict with PQC readiness requirements. Alternatively, restrict TLS client connections to trusted, authenticated servers using certificate pinning or a private PKI, which prevents the malicious-server scenario but does not eliminate the defect and adds operational complexity for certificate rotation.
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Same weakness CWE-416 – Use After Free
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External POC / Exploit Code
Leaving vuln.today