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Partial-chain certificate trust bypass in wolfSSL
CVE-2026-6091 is a certificate-validation vulnerability in wolfSSL's OpenSSL compatibility certificate-path-building implementation involving wolfSSL_X509_verify_cert and X509_STORE. In builds using OPENSSL_EXTRA, enabling X509_V_FLAG_PARTIAL_CHAIN may cause verification to accept a certificate chain terminating at a peer-supplied, untrusted intermediate certificate rather than a configured trusted anchor. An attacker can present a chain ending at an intermediate certificate they control and have it accepted as valid, bypassing certificate trust validation.
What it means and what to do now: patch path, interim mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
Applications using the affected verification configuration may trust attacker-controlled certificates without establishing a chain to a configured trust anchor. This can enable peer impersonation and man-in-the-middle attacks, potentially compromising the confidentiality and integrity of communications that rely on the affected certificate verification.
If you can’t patch tonight, do this now.
Disable X509_V_FLAG_PARTIAL_CHAIN in affected verification configurations. Where feasible, disable or avoid the OpenSSL compatibility certificate-path-building implementation under OPENSSL_EXTRA until the fix is applied.
Patch, then assume compromise.
Apply the vendor-provided certificate-path validation fix or upgrade to a wolfSSL release containing it. For affected Alpine Linux installations, update the wolfssl library and related packages to version 5.9.2-r0 or later. Rebuild and redeploy applications or firmware that embed the vulnerable library. The exact first fixed upstream wolfSSL version is not established by the available information.
No public exploits tracked yet. Mallory keeps watching.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.