{"id":"CVE-2026-63073","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-63073","summary":"Untrusted Sender DN Used as Format String in CMP Response Validation","details":"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.","published":"2026-08-25T12:59:43.356Z","modified":"2026-09-01T03:46:08.324838027Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[],"fix":{"url":"https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca","label":"openssl/openssl@0cc20b3"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63073.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63073"},{"type":"ADVISORY","url":"https://openssl-library.org/news/secadv/20260825.txt"},{"type":"FIX","url":"https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca"},{"type":"FIX","url":"https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29"},{"type":"FIX","url":"https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21"},{"type":"FIX","url":"https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-01T03:46:08.324838027Z"}}