EUVD-2026-39565
GHSA-5hpf-pc4x-3jcf
Severity by source
CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/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
AV:N reflects network-facing JWT and auth service use cases; AC:H captures OPENSSL_EXTRA build prerequisite; no confidentiality or availability impact.
Primary rating from Vendor (wolfSSL).
CVSS VectorVendor: wolfSSL
CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/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
Lifecycle Timeline
2DescriptionCVE.org
HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag could be accepted as valid during HMAC verification. In the OpenSSL-compatibility HMAC verify path the supplied signature length was only checked as not exceeding the MAC length, so a zero-length or otherwise truncated tag could pass verification. The fix requires the supplied tag length to exactly equal the MAC length and rejects a zero-length MAC, so a forged short or empty tag is no longer accepted.
AnalysisAI
HMAC tag forgery in wolfSSL's OpenSSL-compatibility layer allows a zero-length or arbitrarily truncated HMAC tag to pass verification in EVP_DigestVerifyFinal, undermining message authentication for any application relying on this API path. Applications compiled with the OPENSSL_EXTRA flag that use EVP_DigestVerifyFinal for HMAC verification - including JWT validation libraries and message authentication flows - are affected across all currently-known wolfSSL versions. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The target application must be compiled against wolfSSL with the OPENSSL_EXTRA build-time flag explicitly set, and must not have NO_HMAC or NO_SHA256 disabled. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The official CVSS 4.0 vector scores this at 2.1 (Low): AV:L/AC:H/AT:P/PR:N/UI:N with integrity-only impact (VI:L). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker targeting a network-accessible service that uses wolfSSL with OPENSSL_EXTRA for JWT or HMAC-based message authentication submits a crafted token or message with a zero-length or empty HMAC signature field. The vulnerable EVP_DigestVerifyFinal code path accepts the zero-length tag as valid because the length check does not require equality with the full MAC size, causing the application to treat the unauthenticated message as legitimately signed. … |
| Remediation | The upstream fix is available as GitHub PR #10192 at https://github.com/wolfSSL/wolfssl/pull/10192, which enforces strict tag-length equality in EVP_DigestVerifyFinal. … Detailed patch versions, workarounds, and compensating controls in full report. |
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