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.
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.
Metrics
Affected Vendors & Products
No data.
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Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Tue, 25 Aug 2026 13:15:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | Untrusted Sender DN Used as Format String in CMP Response Validation | |
| Weaknesses | CWE-134 | |
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: openssl
Published:
Updated: 2026-08-25T12:59:43.356Z
Reserved: 2026-07-15T13:10:26.188Z
Link: CVE-2026-63073
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-08-25T13:19:26.147
Modified: 2026-08-25T13:19:26.147
Link: CVE-2026-63073
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses