OpenSSL CMP Use of Externally-Controlled Format String Information Disclosure Vulnerability

October 22nd, 2026
ZDI-26-789 ZDI-CAN-30379

CVE ID

CVE-2026-63073

CVSS Score

6.5 AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:L

Affected Vendors

OpenSSL

Affected Products

OpenSSL

Vulnerability Details

This vulnerability allows remote attackers to disclose sensitive information on affected installations of OpenSSL. Authentication is not required to exploit this vulnerability.

The specific flaw exists within the handling of Distinguished Names within CMP messages. The issue results from the lack of proper validation of a user-supplied string before using it as a format specifier. An attacker can leverage this vulnerability to disclose information in the context of the client or server.

Additional Details

OpenSSL has issued an update to correct this vulnerability. More details can be found at:
https://openssl-library.org/news/vulnerabilities/#CVE-2026-63073

Disclosure Timeline

  • 2026-04-08 - Vulnerability reported to vendor
  • 2026-10-22 - Coordinated public release of advisory
  • 2026-10-22 - Advisory Updated

Credit

TrendAI Zero Day Initiative

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