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

Vulnerability from cvelistv5 – Published: 2026-08-25 12:59 – Updated: 2026-08-25 12:59
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
No CVSS data available.
CWE
  • CWE-134 - Use of Externally-Controlled Format String
Assigner
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)
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    "dateReserved": "2026-07-15T13:10:26.188Z",
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      "current_release_date": "2026-08-27T08:00:43+00:00",
      "cve": "CVE-2026-63073",
      "id": "CVE-2026-63073",
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      "product_status:fixed": "6",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "openssl: untrusted sender DN used as format string in CMP response validation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63073.json",
      "version": "3"
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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  • 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.
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  • 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.