Vulnerability-Lookup

GHSA-826X-QG76-XQJX

Vulnerability from github – Published: 2026-08-25 15:32 – Updated: 2026-08-25 15:32

Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-63073"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-134"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-25T13:19:26Z",
    "severity": null
  },
  "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.",
  "id": "GHSA-826x-qg76-xqjx",
  "modified": "2026-08-25T15:32:59Z",
  "published": "2026-08-25T15:32:58Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63073"
    },
    {
      "type": "WEB",
      "url": "https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca"
    },
    {
      "type": "WEB",
      "url": "https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29"
    },
    {
      "type": "WEB",
      "url": "https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21"
    },
    {
      "type": "WEB",
      "url": "https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4"
    },
    {
      "type": "WEB",
      "url": "https://openssl-library.org/news/secadv/20260825.txt"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

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

Vulnerability from cvelistv5 – Published: 2026-08-25 12:59 – Updated: 2026-08-25 12:59

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

No CVSS data available.

CWE

CWE-134 - Use of Externally-Controlled Format String

Assigner

openssl mitre root

References

5 references

URL	Tags
https://openssl-library.org/news/secadv/20260825.txt	vendor-advisory
https://github.com/openssl/openssl/commit/7eb2e3e…	patch
https://github.com/openssl/openssl/commit/6a0acc0…	patch
https://github.com/openssl/openssl/commit/0cc20b3…	patch
https://github.com/openssl/openssl/commit/a7e5a6e…	patch

Impacted products

1 product

Vendor	Product	Version
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)

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

JSON

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          "vendor": "OpenSSL",
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              "lessThan": "4.0.2",
              "status": "affected",
              "version": "4.0.0",
              "versionType": "semver"
            },
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              "lessThan": "3.6.4",
              "status": "affected",
              "version": "3.6.0",
              "versionType": "semver"
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            },
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          "type": "reporter",
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          "lang": "en",
          "type": "reporter",
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        },
        {
          "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",
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
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              "type": "text/html",
              "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."
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          "name": "3.4.7 git commit",
          "tags": [
            "patch"
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          "url": "https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4"
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    "datePublished": "2026-08-25T12:59:43.356Z",
    "dateReserved": "2026-07-15T13:10:26.188Z",
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}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

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GHSA-826X-QG76-XQJX

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

Tags

Sightings

Nomenclature