CVE-2026-63073Network attack vector

CMP client crash via sender DN format string

Published Aug 25, 2026 · Updated Aug 25, 2026

Format string injection in OpenSSL 3.4, 3.5, 3.6, and 4.0 allows remote attackers to crash CMP clients through a malicious sender DN. ossl_cmp_msg_check_update() converts the peer DN with X509_NAME_oneline() and passes it directly to ERR_raise_data() as the format argument. The path requires an expected sender or pinned server certificate; unmatched %s or %n directives consume unrelated stack values and terminate the client.

CVSS severity5.9
Medium
EPSS probability0.93%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Format string injection in OpenSSL 3.4, 3.5, 3.6, and 4.0 allows remote attackers to crash CMP clients through a malicious sender DN. ossl_cmp_msg_check_update() converts the peer DN with X509_NAME_oneline() and passes it directly to ERR_raise_data() as the format argument. The path requires an expected sender or pinned server certificate; unmatched %s or %n directives consume unrelated stack values and terminate the client.

The record

CVE
CVE-2026-63073
Published
Aug 25, 2026
Updated
Aug 25, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-134, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8CVE.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
5.9Red HatCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-134Use of Externally-Controlled Format String
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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