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Fencer Vulns
critical 9.8

CVE-2026-63073 in the critical feed json

Untrusted Sender DN Used as Format String in CMP Response Validation

published 2026-08-25 2 mo ago modified 2026-09-11 58 d ago also EUVD-2026-65483

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 67%
public exploits
0
none known

Summary

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.

Patch / fix

  • OpenSSL OpenSSL 3.4.7, 3.5.8, 3.6.4, 4.0.2
  • openssl Debian 13 3.5.7-1~deb13u2
  • openssl Debian 14 3.6.4-1

debian advisories DEBIAN-CVE-2026-63073

  • openssl Ubuntu 26.04 LTS 3.5.5-1ubuntu3.4

ubuntu advisories UBUNTU-CVE-2026-63073

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • openssl RHEL 9 1:3.5.8-1.el9_8
  • openssl-libs RHEL 9 1:3.5.8-1.el9_8
  • openssl-perl RHEL 9 1:3.5.8-1.el9_8
  • openssl RHEL 10.2 1:3.5.8-1.el10_2
  • openssl-libs RHEL 10.2 1:3.5.8-1.el10_2
  • openssl-perl RHEL 10.2 1:3.5.8-1.el10_2
  • openssl3 hummingbird 1 3.5.8-0.1.hum1
  • openssl3-libs hummingbird 1 3.5.8-0.1.hum1

red hat advisories RHSA-2026:67165RHSA-2026:67154RHSA-2026:59635RHSA-2026:59641

  • openssl-3 SLE Module for Basesystem 15 SP7 3.5.0-150700.5.50.1
  • openssl-3 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 3.5.0-160000.10.1

suse advisories SUSE-SU-2026:4039-1SUSE-SU-2026:23463-1SUSE-SU-2026:23609-1

  • openssl-3 openSUSE Leap 16.0 3.5.0-160000.10.1
  • openssl-3 openSUSE Tumbleweed 3.5.3-8.1

opensuse advisories openSUSE-SU-2026:21744-1openSUSE-SU-2026:11623-1

  • openssl AlmaLinux 10 1:3.5.8-1.el10_2.alma.1
  • openssl-libs AlmaLinux 10 1:3.5.8-1.el10_2.alma.1
  • openssl-perl AlmaLinux 10 1:3.5.8-1.el10_2.alma.1
  • openssl AlmaLinux 9 1:3.5.8-1.el9_8
  • openssl-libs AlmaLinux 9 1:3.5.8-1.el9_8
  • openssl-perl AlmaLinux 9 1:3.5.8-1.el9_8

almalinux advisories ALSA-2026:67154ALSA-2026:67165

  • openssl Rocky Linux 9 1:3.5.8-1.el9_8
  • openssl Rocky Linux 10 1:3.5.8-1.el10_2

rocky linux advisories RLSA-2026:67165RLSA-2026:67154

  • openssl Alpine 3.21 3.3.7-r1
  • openssl Alpine 3.24, Alpine 3.23, Alpine 3.22 3.5.8-r0

alpine advisories ALPINE-CVE-2026-63073

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • openssl Azure Linux 3.0 3.3.7-6

azure linux advisories AZL-97950

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-63073 updated cvss 5.9

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

  • Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9 Red Hat Enterprise Linux 10 edk2 Red Hat JBoss Core Services jbcs-httpd24-openssl, jbcs-httpd24-openssl-libs, jbcs-httpd24-openssl-perl, jbcs-openssl-win6-x86_64.zip 3.5.5-SP4 Red Hat JBoss Web Server 6 jws-optional-native-components-win6-x86_64.zip 6.2.4.ER1 Red Hat JBoss Web Server 7 jws-optional-native-components-win6-x86_64.zip 6.2.4.ER1 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-9
    +1 more products
    Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/cert-manager-operator-rhel9 1790272426, cert-manager/cert-manager-operator-rhel9 1790589855, cert-manager/jetstack-cert-manager-rhel9 1790223279, cert-manager/jetstack-cert-manager-rhel9 1790589912, cert-manager/cert-manager-istio-csr-rhel9 1790223719, cert-manager/cert-manager-istio-csr-rhel9 1790589914, +1 more
    fixed: vendor fix RHSA-2026:72475
  • Red Hat Enterprise Linux AppStream (v. 9) openssl-perl 3.5.8-1.el9_8
    fixed: vendor fix RHSA-2026:67165
  • Red Hat Enterprise Linux AppStream (v. 10) openssl-perl 3.5.8-1.el10_2
    fixed: vendor fix RHSA-2026:67154
  • Red Hat Enterprise Linux BaseOS (v. 9) openssl 3.5.8-1.el9_8, openssl-libs 3.5.8-1.el9_8
    fixed: vendor fix RHSA-2026:67165
  • Red Hat Enterprise Linux BaseOS (v. 10) openssl 3.5.8-1.el10_2, openssl-libs 3.5.8-1.el10_2
    fixed: vendor fix RHSA-2026:67154
  • Red Hat Hardened Images openssl 3.5.8-0.1.hum1, openssl3 3.5.8-0.1.hum1, openssl-libs 3.5.8-0.1.hum1, openssl-perl 3.5.8-0.1.hum1, openssl3-libs 3.5.8-0.1.hum1, openssl-config-fips 3.5.8-0.1.hum1, +3 more
    fixed: vendor fix RHSA-2026:59641
  • Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1790241954, rhui5/rhua-rhel9 1790242004, rhui5/haproxy-rhel9 1790241900, rhui5/installer-rhel9 1789482961, rhui5/cds-kubernetes-rhel9 1789479916
    fixed: vendor fix RHSA-2026:67956
show 1 more
  • Red Hat Cert Manager support for Red Hat OpenShift release 1.20 cert-manager/jetstack-cert-manager-acmesolver-rhel9 1790223630 Red Hat Enterprise Linux 6 openssl, openssl-perl Red Hat Enterprise Linux 7 ovmf, OVMF, shim, AAVMF, mokutil, openssl, +5 more Red Hat Enterprise Linux 8 edk2, shim, openssl, shim-x64, edk2-ovmf, shim-aa64, +10 more Red Hat Enterprise Linux 9 edk2, shim, shim-x64, edk2-ovmf, shim-aa64, edk2-tools, +4 more Red Hat Enterprise Linux 10 shim, shim-unsigned-x64, shim-unsigned-aarch64
    +6 more products
    Red Hat Hardened Images unbound Red Hat OpenShift AI (RHOAI) rhoai/odh-llama-stack-k8s-operator-rhel9 Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8 Red Hat Satellite 6 puppet-agent, openvox-agent Red Hat Satellite Client puppet-agent, openvox-agent Red Hat Update Infrastructure 5 rhui5/cds-rhel9 1789479900, rhui5/rhua-rhel9 1789478095, rhui5/haproxy-rhel9 1789479891, rhui5/installer-rhel9 1790241922, rhui5/cds-kubernetes-rhel9 1790241897
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
2 mo ago

Exploit prediction

1.16% chance of exploitation in the next 30 days, higher than 67% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

  • OpenSSL OpenSSL

Classification

Weakness
  • CWE-134 Use of Externally-Controlled Format String
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.