CVE-2026-63073 (GCVE-0-2026-63073)

Vulnerability from cvelistv5 – Published: 2026-08-25 12:59 – Updated: 2026-08-31 19:12
VLAI
Title
Untrusted Sender DN Used as Format String in CMP Response Validation
Summary
Issue summary: OpenSSL CMP response validation passed an unexpected response sender distinguished name directly as the format string to `ERR_raise_data()`. Impact summary: A malicious or intercepted CMP endpoint can crash a CMP client that enforces an expected sender or uses a pinned server certificate whose subject becomes the default expected sender. CWE: CWE-134 (Use of Externally-Controlled Format String) Description: When validating a received CMP message, ossl_cmp_msg_check_update() converts the peer-supplied sender distinguished name with X509_NAME_oneline() and passes it directly as the format argument to ERR_raise_data(). Percent characters survive the conversion, so a sender DN such as "CN=%s%n" reaches BIO_vsnprintf() as an attacker-controlled format string with no matching variadic arguments. This path is only reached when the caller configures an expected sender or pins a server certificate, which is the normal configuration for a CMP client validating server responses. Since the attacker controls the format string but none of the variadic arguments, such specifiers as %s and %n dereference or write through unrelated stack contents and crash the client. The reliable consequence is a denial of service, when the response comes from a malicious or intercepted CMP endpoint. There is no controlled memory write, arbitrary-address read, or reliable path to remote code execution. FIPS impact: no No FIPS modules are affected by this issue, as the CMP protocol implementation is outside the OpenSSL FIPS module boundary.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: yes Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-31 19:12 UTC
CWE
  • CWE-134 - Use of Externally-Controlled Format String
Assigner
openssl CNA under the mitre root
CNA scorecard B 78/100 over 43 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
OpenSSL OpenSSL Affected: 4.0.0 , < 4.0.2 (semver)
Affected: 3.6.0 , < 3.6.4 (semver)
Affected: 3.5.0 , < 3.5.8 (semver)
Affected: 3.4.0 , < 3.4.7 (semver)
guessed Create a notification for this product.
Date Public
2026-08-25 11:36
Credits
Filipe Casal (Trail of Bits) Brandon Luo TrendAI Zero Day Initiative Filipe Casal (Trail of Bits)
Show details on NVD website
To clipboard 

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                  "value": "Issue summary: OpenSSL CMP response validation passed an unexpected response\u003cbr\u003esender distinguished name directly as the format string to `ERR_raise_data()`.\u003cbr\u003e\u003cbr\u003eImpact summary: A malicious or intercepted CMP endpoint can crash a CMP client\u003cbr\u003ethat enforces an expected sender or uses a pinned server certificate whose\u003cbr\u003esubject becomes the default expected sender.\u003cbr\u003e\u003cbr\u003eCWE: CWE-134 (Use of Externally-Controlled Format String)\u003cbr\u003e\u003cbr\u003eDescription: When validating a received CMP message, ossl_cmp_msg_check_update()\u003cbr\u003econverts the peer-supplied sender distinguished name with X509_NAME_oneline()\u003cbr\u003eand passes it directly as the format argument to ERR_raise_data(). Percent\u003cbr\u003echaracters survive the conversion, so a sender DN such as \"CN=%s%n\" reaches\u003cbr\u003eBIO_vsnprintf() as an attacker-controlled format string with no matching variadic\u003cbr\u003earguments. This path is only reached when the caller configures an expected\u003cbr\u003esender or pins a server certificate, which is the normal configuration for a\u003cbr\u003eCMP client validating server responses.\u003cbr\u003e\u003cbr\u003eSince the attacker controls the format string but none of the variadic\u003cbr\u003earguments, such specifiers as %s and %n dereference or write through unrelated\u003cbr\u003estack contents and crash the client. The reliable consequence is a denial of\u003cbr\u003eservice, when the response comes from a malicious or intercepted CMP endpoint.\u003cbr\u003eThere is no controlled memory write, arbitrary-address read, or reliable path\u003cbr\u003eto remote code execution.\u003cbr\u003e\u003cbr\u003eFIPS impact: no\u003cbr\u003e\u003cbr\u003eNo FIPS modules are affected by this issue, as the CMP protocol\u003cbr\u003eimplementation is outside the OpenSSL FIPS module boundary."
                }
              ],
              "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."
            }
          ],
          "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": {
            "dateUpdated": "2026-08-25T12:59:43.356Z",
            "orgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
            "shortName": "openssl"
          },
          "references": [
            {
              "name": "OpenSSL Advisory",
              "tags": [
                "vendor-advisory"
              ],
              "url": "https://openssl-library.org/news/secadv/20260825.txt"
            },
            {
              "name": "4.0.2 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21"
            },
            {
              "name": "3.6.4 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29"
            },
            {
              "name": "3.5.8 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca"
            },
            {
              "name": "3.4.7 git commit",
              "tags": [
                "patch"
              ],
              "url": "https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4"
            }
          ],
          "source": {
            "discovery": "UNKNOWN"
          },
          "title": "Untrusted Sender DN Used as Format String in CMP Response Validation",
          "x_generator": {
            "engine": "Vulnogram 0.2.0"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "3a12439a-ef3a-4c79-92e6-6081a721f1e5",
        "assignerShortName": "openssl",
        "cveId": "CVE-2026-63073",
        "datePublished": "2026-08-25T12:59:43.356Z",
        "dateReserved": "2026-07-15T13:10:26.188Z",
        "dateUpdated": "2026-08-31T19:12:54.136Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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