CVE-2026-94418: Signature failure masked by date error under WOLFSSL_SMALL_CERT_VERIFY
Under WOLFSSLSMALLCERTVERIFY, ProcessPeerCertParse() runs the certificate signature check separately from the parse to keep peak memory down, then merges the two results, but it merged the signature result back only when the parse returned 0, so any parse error hid it. ParseCertRelative() reaches its validity-date, name-constraint and critical-extension checks only after ConfirmSignature() has passed, so splitting the signature check out inverts the precedence that makes "override date errors" a sound policy, and ASNSIGCONFIRME is never surfaced anywhere. The attacker needs no key material from the real PKI and no CA compromise: a self-made certificate carrying the expected subject name, the trusted CA's subject as its issuer, arbitrary bytes where the signature goes, a validity window in the past and the attacker's own key pair is sufficient. Affected builds define WOLFSSLSMALLCERTVERIFY, which is off by default, is not set implicitly by any platform or preset header, and is not reachable from any CMake option; the autotools routes are --enable-lowresource, --enable-leantls, --enable-tinytls13=cert and --enable-tinytls13=mutualauth, and examples/configs/usersettingsembedded.h reaches it through WCCFGSMALLCERTVERIFY, which ships as 0, while neither --enable-all nor --enable-distro enables it at all. The application must additionally install a verify callback through wolfSSLCTXsetverify() or wolfSSLsetverify() with WOLFSSLVERIFYPEER that returns 1 for ASNBEFOREDATEE or ASNAFTERDATEE; wolfSSL ships this exact shape as myVerify() in wolfssl/test.h under VERIFYOVERRIDEDATEERR, which examples/client -D selects. An application with no callback, or whose callback returns preverify for date errors, still fails the handshake, and wolfSSLCertManagerVerifyBuffer() and wcCheckCertSignature() report ASNSIGCONFIRME correctly in the same binary. TLS 1.2 and TLS 1.3 are affected in both directions, and DTLS reaches the same function; where the forged certificate is a chain certificate the callback's consent causes it to be cached in the WOLFSSLCTX certificate manager, so an exposed deployment must restart the context or the process rather than merely reconnect.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Operational
If an exposed deployment may have cached a forged chain certificate in the WOLFSSL_CTX certificate manager, restart the WOLFSSL_CTX or the process; merely reconnecting is insufficient.
Event History
Frequently Asked Questions
Which deployments are exposed?
Only builds that define WOLFSSL_SMALL_CERT_VERIFY are affected. This setting is off by default, is not implicitly enabled by platform or preset headers, and is not reachable through a CMake option; the listed autotools routes include --enable-lowresource, --enable-leantls, --enable-tinytls13=cert, and --enable-tinytls13=mutualauth.
What must an attacker provide to exploit this?
The attacker can use a self-made certificate with the expected subject name, the trusted CA subject as issuer, arbitrary signature bytes, an expired validity window, and the attacker’s own key pair. No real PKI private key material or CA compromise is required.
How can I determine whether my build is affected?
Check whether WOLFSSL_SMALL_CERT_VERIFY is defined in the build configuration or generated compiler settings. For autotools builds, review whether one of the listed low-resource or tiny-TLS certificate options was used.