{"id":"CVE-2026-5501","state":"PUBLISHED","title":"Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates","description":"wolfSSL_X509_verify_cert in the OpenSSL compatibility layer accepts a certificate chain in which the leaf's signature is not checked, if the attacker supplies an untrusted intermediate with Basic Constraints `CA:FALSE` that is legitimately signed by a trusted root. An attacker who obtains any leaf certificate from a trusted CA (e.g. a free DV cert from Let's Encrypt) can forge a certificate for any subject name with any public key and arbitrary signature bytes, and the function returns `WOLFSSL_SUCCESS` / `X509_V_OK`. The native wolfSSL TLS handshake path (`ProcessPeerCerts`) is not susceptible and the issue is limited to applications using the OpenSSL compatibility API directly, which would include integrations of wolfSSL into nginx and haproxy.","publishedAt":"2026-04-10T03:07:39.604Z","updatedAt":"2026-04-22T13:59:28.514Z","severity":{"score":8.6,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","source":"wolfSSL"},"assigner":"wolfSSL","products":["wolfSSL wolfSSL"],"affected":[{"vendor":"wolfSSL","product":"wolfSSL","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThanOrEqual":"5.9.0","versionType":"semver"}],"modules":["wolfSSL_X509_verify_cert"],"programFiles":["src/x509_str.c"]}],"references":["https://github.com/wolfSSL/wolfssl/pull/10102"],"weaknesses":["CWE-295"],"ingestedAt":"2026-10-29T20:12:32.778Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/5xxx/CVE-2026-5501.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-5501","state":"PUBLISHED","datePublished":"2026-04-10T03:07:39.604Z","dateUpdated":"2026-04-22T13:59:28.514Z","assignerShortName":"wolfSSL","assignerOrgId":"50d2cd11-d01a-48ed-9441-5bfce9d63b27","dateReserved":"2026-04-03T15:46:09.302Z"},"containers":{"cna":{"title":"Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates","descriptions":[{"lang":"en","value":"wolfSSL_X509_verify_cert in the OpenSSL compatibility layer accepts a certificate chain in which the leaf's signature is not checked, if the attacker supplies an untrusted intermediate with Basic Constraints `CA:FALSE` that is legitimately signed by a trusted root. An attacker who obtains any leaf certificate from a trusted CA (e.g. a free DV cert from Let's Encrypt) can forge a certificate for any subject name with any public key and arbitrary signature bytes, and the function returns `WOLFSSL_SUCCESS` / `X509_V_OK`. The native wolfSSL TLS handshake path (`ProcessPeerCerts`) is not susceptible and the issue is limited to applications using the OpenSSL compatibility API directly, which would include integrations of wolfSSL into nginx and haproxy."}],"affected":[{"vendor":"wolfSSL","product":"wolfSSL","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThanOrEqual":"5.9.0","versionType":"semver"}],"modules":["wolfSSL_X509_verify_cert"],"programFiles":["src/x509_str.c"]}],"references":[{"url":"https://github.com/wolfSSL/wolfssl/pull/10102"}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"LOW","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","subConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","subIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED","version":"4.0","baseSeverity":"HIGH","baseScore":8.6,"vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-295","lang":"en","description":"CWE-295 Improper certificate validation","type":"CWE"}]}],"providerMetadata":{"shortName":"wolfSSL","orgId":"50d2cd11-d01a-48ed-9441-5bfce9d63b27","dateUpdated":"2026-04-10T03:07:39.604Z"},"credits":[{"lang":"en","value":"Calif.io in collaboration with Claude and Anthropic Research","type":"finder"}],"source":{"discovery":"EXTERNAL"},"x_generator":{"engine":"Vulnogram 1.0.1"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-04-22T03:55:48.544190Z","id":"CVE-2026-5501","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-04-22T13:59:28.514Z"}}]}}}