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No exploitation reportedFix available

CVE-2026-63073

No exploitation reported by the sources we read.

  • Published2026-08-25
  • Fixed in4.0.2 · 3.6.4 · 3.5.8 · 3.4.7
  • WeaknessCWE-134

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2026-08-2513:19CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-63073?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-63073?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
OpenSSL
BranchAffectedFixed in
4.0≥ 4.0.0, < 4.0.24.0.2
3.6≥ 3.6.0, < 3.6.43.6.4
3.5≥ 3.5.0, < 3.5.83.5.8
3.4≥ 3.4.0, < 3.4.73.4.7

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • opensslAlmaLinux:10all versions · fixed in 1:3.5.8-1.el10_2.alma.1and 3 other packages
  • opensslAlmaLinux:9all versions · fixed in 1:3.5.8-1.el9_8and 3 other packages

Vendor advisories

  • CVE-2026-63073 Red Hat Product Security145 products fixed · 16 known affected

    openssl: untrusted sender DN used as format string in CMP response validation

    rhdh/rhdh-hub-rhel9 as a component of Red Hat Developer Hub · edk2-aarch64 as a component of Red Hat Enterprise Linux 10 · edk2-ovmf as a component of Red Hat Enterprise Linux 10 · +13 more

  • RHSA-2026:72476 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1

  • RHSA-2026:72475 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1

  • RHSA-2026:72470 Red Hat Product Security8 products fixed

    Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1

  • RHSA-2026:72399 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1

  • RHSA-2026:72395 Red Hat Product Security4 products fixed

    Red Hat Security Advisory: cert-manager Operator for Red Hat OpenShift 1.20.1

7 more advisories

Full record on NVD

Fix

  1. Update OpenSSL to 4.0.2 · 3.6.4 · 3.5.8 · 3.4.7
  2. Vendor fix Red Hat Product Security RHSA-2026:72476 · 4 productsBefore applying this update, make sure all previously released errata relevant to your system have been applied. The steps to apply the upgraded images are different depending on the installation plan approval policy you used when installing the cert-manager Operator for Red Hat OpenShift. - If t…
  3. Vendor fix Red Hat Product Security RHSA-2026:71603 · 3 productsThe container images provided by this release, apart from the installer, should be deployed using rhui-installer utility. See the official documentation for more details.
  4. Vendor fix Red Hat Product Security RHSA-2026:67165 · 49 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  5. Vendor fix Red Hat Product Security RHSA-2026:59641 · 15 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
  6. Workaround from the vendor Red Hat Product Security RHSA-2026:72476 · 4 productsMitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionnone2026-08-31
  • OpenCVESSVC decisionnone—
  • CISA-ADPCVSS 3.19.82026-08-31
  • CNAweakness (CWE)CWE-134read 2026-10-23
  • FIRST EPSSEPSS score1.2 %2026-10-22
  • OSVaffected packages—

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2026-08-25
Last Modified
2026-09-11
NVD status
Analyzed

Frequently asked questions

What is CVE-2026-63073?

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.

Is CVE-2026-63073 actively exploited?

Active exploitation of CVE-2026-63073 has not been confirmed. Its EPSS score was 1.2% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-63073?

CVE-2026-63073 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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