HighCVE-2026-63073

    Untrusted Sender DN Used as Format String in CMP Response Validation (CVE-2026-63073)

    Published Last modified Sources: Red Hat, SUSE, Ubuntu, Debian, CVE.org, Msrc Update Guide, BSI

    What is affected, what to do

    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.

    Update OpenSSL to version 4.0.2, OpenSSL to version 3.6.4, OpenSSL to version 3.5.8.

    Affected
    • OpenSSL lt 4.0.0..4.0.2
    • OpenSSL lt 3.6.0..3.6.4
    • OpenSSL lt 3.5.0..3.5.8
    • OpenSSL lt 3.4.0..3.4.7
    Fixed in
    • OpenSSL 4.0.2
    • OpenSSL 3.6.4
    • OpenSSL 3.5.8
    • OpenSSL 3.4.7

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.4

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.4

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, SUSE, Ubuntu, Debian, CVE.org, Msrc Update Guide, BSI

    1.2 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 67.0

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    97.36 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.4 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.4
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    1.2 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    67.0
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-134

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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.

    Source: redhat_csaf, suse_csaf, Ubuntu Security Notices, Debian Security Advisories, NVD (NIST), cvelistv5, Microsoft Security Update Guide, BSI WID Portal, BSI CSAF

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    OpenSSLOpenSSL
    • 3.6.0 – < 3.6.4
    • 3.4.0 – < 3.4.7
    • 4.0.0 – < 4.0.2
    • 3.5.0 – < 3.5.8
    • 3.6.4
    • 3.4.7
    • 4.0.2
    • 3.5.8
    opensslopenssl
    • 3.5.0 – < 3.5.8
    • 3.4.0 – < 3.4.7
    • 4.0.0 – < 4.0.2
    • 3.6.0 – < 3.6.4
    • 3.5.8
    • 3.4.7
    • 4.0.2
    • 3.6.4
    FreeBSD ProjectFreeBSD OS
    • < 15.1-STABLE
    • < 14.4-STABLE
    • < 15.0-RELEASE-p13
    • < 14.4-RELEASE-p9
    • < 15.1-RELEASE-p3
    • 15.1-STABLE
    • 14.4-STABLE
    • 15.0-RELEASE-p13
    • 14.4-RELEASE-p9
    • 15.1-RELEASE-p3
    MeinbergLANTIME
    • < V7.10.016
    • V7.10.016
    Open SourceOpenSSL
    • < 3.4.7
    • < 4.0.2
    • < 3.5.8
    • < 3.6.4
    • < 3.0.22
    • < 1.1.1zi
    • < 1.0.2zr
    • 3.4.7
    • 4.0.2
    • 3.5.8
    • 3.6.4
    • 3.0.22
    • 1.1.1zi
    • 1.0.2zr

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianopenssltrixie
    Linuxubuntuopenssljammy
    Linuxubuntuopensslnoble
    Linuxubuntuopensslresolute

    Weakness classes (CWE)

    • CWE-134Use of Externally-Controlled Format String

      Base

      The product uses a function that accepts a format string as an argument, but the format string originates from an external source.

      Entry at MITRE CWE-134

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Initial analysis by NVDNVD

      Newly listed as affected:
      • OpenSSL (3.5.0 – before 3.5.8; 3.6.0 – before 3.6.4; 4.0.0 – before 4.0.2; 3.4.0 – before 3.4.7)
      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationadded
      —
      OR *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.5.0 up to (excluding) 3.5.8 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.6.0 up to (excluding) 3.6.4 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 4.0.0 up to (excluding) 4.0.2 *cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:* versions from (including) 3.4.0 up to (excluding) 3.4.7
      Reference typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29 Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21 Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4 Types: Patch
      Reference typeadded
      —
      OpenSSL Software Foundation: https://openssl-library.org/news/secadv/20260825.txt Types: Vendor Advisory

      Source identifier: nvd@nist.gov

    2. Record modifiedopenssl.org

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4
      Referenceadded
      —
      https://openssl-library.org/news/secadv/20260825.txt
      Referenceremoved
      https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca
      —
      Referenceremoved
      https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29
      —
      Referenceremoved
      https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21
      —
      Referenceremoved
      https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4
      —
      Referenceremoved
      https://openssl-library.org/news/secadv/20260825.txt
      —

      Source identifier: openssl-security@openssl.org

    3. Record modifiedCISA ADP

      CVSS V3.1: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

      CISA assessment (SSVC): exploitation: none known, automatable: yes

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
      SSVC assessmentadded
      —
      {"id":"CVE-2026-63073","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-31T19:12:48.434586Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    4. Receivedopenssl.org

      Weakness type: CWE-134

      Description added or changed

      Show 8 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      OpenSSL
      Descriptionadded
      —
      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.
      Weakness type (CWE)added
      —
      CWE-134
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/0cc20b322639919aa423e90799d9a57c3b4b76ca
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/6a0acc072b4d37a7cac1252a29c1ce1f00c5ec29
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/7eb2e3ec9d1d4f35c8022fccd4b03398b3f33e21
      Referenceadded
      —
      https://github.com/openssl/openssl/commit/a7e5a6eea8fd3ccca6b6fbba031a5fbf8a3d93b4
      Referenceadded
      —
      https://openssl-library.org/news/secadv/20260825.txt

      Source identifier: openssl-security@openssl.org

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