DEBIAN-CVE-2026-63073

Issue summary: OpenSSL CMP response validation passed an unexpected response sender distinguished name directly as the format string to ERRraisedata().  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, osslcmpmsgcheckupdate() converts the peer-supplied sender distinguished name with X509NAMEoneline() and passes it directly as the format argument to ERRraisedata(). 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.