Bug 2517565 (CVE-2026-63073)

Summary: CVE-2026-63073 openssl: untrusted sender DN used as format string in CMP response validation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: abarbaro, akhatavk, alizardo, anthomas, aos-team-art-private, asdas, csutherl, dpaolell, dsoumis, ehelms, ggainey, jchui, jclere, jdelft, jhe, jpasqual, jupierce, juwatts, jwon, ktsao, lgarciaa, mbiarnes, mdellweg, mhulan, nboldt, nmoumoul, oaljalju, osousa, pcreech, pjindal, plodge, ppalepu, ppostler, prdhamdh, psrna, rchan, rhel-process-autobot, rmaucher, security-response-team, sghai, sidsharm, smallamp, suppawar, szappis, tmalecek, vchlup, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in OpenSSL. A malicious CMP (Certificate Management Protocol) endpoint can send an unexpected distinguished name (DN) directly as the format string argument to ERR_raise_data(), causing the application to dereference and write to unrelated stack contents. This can lead to a crash in the CMP client, resulting in a denial of service.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2523647, 2523648, 2523649, 2523650, 2523651, 2523652    
Bug Blocks:    

Description OSIDB Bzimport 2026-08-17 19:54:48 UTC 
A flaw was found in OpenSSL. OpenSSL CMP response validation passed an unexpected response sender distinguished name directly as the format string to ERR_raise_data().

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.

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.

No FIPS modules are affected by this issue, as the CMP protocol implementation is outside the OpenSSL FIPS module boundary.

OpenSSL 4.0, 3.6, 3.5, and 3.4 are vulnerable to this issue.
OpenSSL 3.0, 1.1.1, and 1.0.2 are not affected by this issue.
OpenSSL 4.0 users should upgrade to OpenSSL 4.0.2.
OpenSSL 3.6 users should upgrade to OpenSSL 3.6.4.
OpenSSL 3.5 users should upgrade to OpenSSL 3.5.8.
OpenSSL 3.4 users should upgrade to OpenSSL 3.4.7.