Format string error in OpenSSL - CVE-2026-63073
Published: August 26, 2026
Vulnerability identifier: #VU145421
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-63073
CWE-ID: CWE-134
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to cause a denial of service.
The vulnerability exists due to use of externally-controlled format string in OpenSSL CMP response validation when processing an unexpected sender distinguished name. A remote attacker can send a crafted CMP response to cause a denial of service.
This path is reached when the client configures an expected sender or uses a pinned server certificate whose subject becomes the default expected sender.
Affected software
OpenSSL
Debian Linux
FreeBSD
openssl (Debian package)
Debian Linux
FreeBSD
openssl (Debian package)
How to mitigate CVE-2026-63073
Install security update from vendor's website.
OpenSSL - addressed in versions 3.4.7, 3.5.8, 3.6.4, 4.0.2
openssl (Debian package) - update to 3.5.7-1~deb13u2
openssl (Debian package) - update to 3.5.7-1~deb13u2