{"id":"CVE-2026-63073","state":"PUBLISHED","title":"Untrusted Sender DN Used as Format String in CMP Response Validation","description":"Issue summary: OpenSSL CMP response validation passed an unexpected response\nsender distinguished name directly as the format string to `ERR_raise_data()`.\n\nImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\nthat enforces an expected sender or uses a pinned server certificate whose\nsubject becomes the default expected sender.\n\nCWE: CWE-134 (Use of Externally-Controlled Format String)\n\nDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\nconverts the peer-supplied sender distinguished name with X509_NAME_oneline()\nand passes it directly as the format argument to ERR_raise_data(). Percent\ncharacters survive the conversion, so a sender DN such as \"CN=%s%n\" reaches\nBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\narguments. This path is only reached when the caller configures an expected\nsender or pins a server certificate, which is the normal configuration for a\nCMP client validating server responses.\n\nSince the attacker controls the format string but none of the variadic\narguments, such specifiers as %s and %n dereference or write through unrelated\nstack contents and crash the client. The reliable consequence is a denial of\nservice, when the response comes from a malicious or intercepted CMP endpoint.\nThere is no controlled memory write, arbitrary-address read, or reliable path\nto remote code execution.\n\nFIPS impact: no\n\nNo FIPS modules are affected by this issue, as the CMP protocol\nimplementation is outside the OpenSSL FIPS module boundary.","publishedAt":"2026-08-25T12:59:43.356Z","updatedAt":"2026-08-31T19:12:54.136Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"CISA-ADP"},"assigner":"openssl","products":["OpenSSL OpenSSL"],"affected":[{"vendor":"OpenSSL","product":"OpenSSL","defaultStatus":"unaffected","versions":[{"version":"4.0.0","status":"affected","lessThan":"4.0.2","versionType":"semver"},{"version":"3.6.0","status":"affected","lessThan":"3.6.4","versionType":"semver"},{"version":"3.5.0","status":"affected","lessThan":"3.5.8","versionType":"semver"},{"version":"3.4.0","status":"affected","lessThan":"3.4.7","versionType":"semver"}]}],"references":["https://openssl-library.org/news/secadv/20260825.txt","https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21","https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29","https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca","https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4"],"weaknesses":["CWE-134"],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63073.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63073","state":"PUBLISHED","datePublished":"2026-08-25T12:59:43.356Z","dateUpdated":"2026-08-31T19:12:54.136Z","assignerShortName":"openssl","assignerOrgId":"3a12439a-ef3a-4c79-92e6-6081a721f1e5","dateReserved":"2026-07-15T13:10:26.188Z"},"containers":{"cna":{"title":"Untrusted Sender DN Used as Format String in CMP Response Validation","descriptions":[{"lang":"en","value":"Issue summary: OpenSSL CMP response validation passed an unexpected response\nsender distinguished name directly as the format string to `ERR_raise_data()`.\n\nImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\nthat enforces an expected sender or uses a pinned server certificate whose\nsubject becomes the default expected sender.\n\nCWE: CWE-134 (Use of Externally-Controlled Format String)\n\nDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\nconverts the peer-supplied sender distinguished name with X509_NAME_oneline()\nand passes it directly as the format argument to ERR_raise_data(). Percent\ncharacters survive the conversion, so a sender DN such as \"CN=%s%n\" reaches\nBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\narguments. This path is only reached when the caller configures an expected\nsender or pins a server certificate, which is the normal configuration for a\nCMP client validating server responses.\n\nSince the attacker controls the format string but none of the variadic\narguments, such specifiers as %s and %n dereference or write through unrelated\nstack contents and crash the client. The reliable consequence is a denial of\nservice, when the response comes from a malicious or intercepted CMP endpoint.\nThere is no controlled memory write, arbitrary-address read, or reliable path\nto remote code execution.\n\nFIPS impact: no\n\nNo FIPS modules are affected by this issue, as the CMP protocol\nimplementation is outside the OpenSSL FIPS module boundary."}],"affected":[{"vendor":"OpenSSL","product":"OpenSSL","defaultStatus":"unaffected","versions":[{"version":"4.0.0","status":"affected","lessThan":"4.0.2","versionType":"semver"},{"version":"3.6.0","status":"affected","lessThan":"3.6.4","versionType":"semver"},{"version":"3.5.0","status":"affected","lessThan":"3.5.8","versionType":"semver"},{"version":"3.4.0","status":"affected","lessThan":"3.4.7","versionType":"semver"}]}],"references":[{"url":"https://openssl-library.org/news/secadv/20260825.txt","name":"OpenSSL Advisory","tags":["vendor-advisory"]},{"url":"https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21","name":"4.0.2 git commit","tags":["patch"]},{"url":"https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29","name":"3.6.4 git commit","tags":["patch"]},{"url":"https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca","name":"3.5.8 git commit","tags":["patch"]},{"url":"https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4","name":"3.4.7 git commit","tags":["patch"]}],"metrics":[{"format":"other","other":{"content":{"text":"Low"},"type":"https://openssl-library.org/policies/general/security-policy/"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-134","description":"Use of Externally-Controlled Format String","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"openssl","orgId":"3a12439a-ef3a-4c79-92e6-6081a721f1e5","dateUpdated":"2026-08-25T12:59:43.356Z"},"credits":[{"lang":"en","type":"reporter","value":"Filipe Casal (Trail of Bits)"},{"lang":"en","type":"reporter","value":"Brandon Luo"},{"lang":"en","type":"reporter","value":"TrendAI Zero Day Initiative"},{"lang":"en","type":"remediation developer","value":"Filipe Casal (Trail of Bits)"}],"datePublic":"2026-08-25T11:36:16.000Z","source":{"discovery":"UNKNOWN"},"x_generator":{"engine":"Vulnogram 0.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"cvssV3_1":{"scope":"UNCHANGED","version":"3.1","baseScore":9.8,"attackVector":"NETWORK","baseSeverity":"CRITICAL","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","integrityImpact":"HIGH","userInteraction":"NONE","attackComplexity":"LOW","availabilityImpact":"HIGH","privilegesRequired":"NONE","confidentialityImpact":"HIGH"}},{"other":{"type":"ssvc","content":{"timestamp":"2026-08-31T19:12:48.434586Z","id":"CVE-2026-63073","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-31T19:12:54.136Z"}}]}}}