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Fencer Vulns
high 7.4

CVE-2026-42790 json

nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification

published 2026-05-27 5 mo ago modified 2026-10-26 14 d ago also EUVD-2026-32558

cvss
7.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 28%
public exploits
0
none known

Summary

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a DNS nameConstraints bypass via subject CommonName fallback in TLS hostname verification.

Two flaws combine to allow a subordinate CA whose DNS nameConstraints are restricted (e.g. permitted;DNS:allowed.example.com) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. victim.example.com):

First, pubkey_cert:validate_names/6 in lib/public_key/src/pubkey_cert.erl only checks SAN DNS entries against nameConstraints. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no subjectAltName therefore trivially satisfies any permitted;DNS:... constraint regardless of its subject commonName.

Second, public_key:pkix_verify_hostname/3 in lib/public_key/src/public_key.erl falls back to the subject commonName when no subjectAltName is present, extracting id-at-commonName attributes as presented IDs and matching them against the reference hostname. The strict pkix_verify_hostname_match_fun(https) matcher does not suppress this fallback.

The result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the nameConstraints are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock ssl:connect with verify_peer, a trusted CA, SNI, and the canonical strict https hostname matcher.

This issue affects OTP from OTP 19.3 before OTP 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 1.4 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.

Patch / fix

  • Erlang OTP 1.15.1.7, 1.17.1.3, 1.20.3.1, 1.21.1, 26.2.5.21, 27.3.4.12, 28.5.0.1, 29.0.1
  • Red Hat Red Hat OpenStack Platform 16.2 0:23.3.4.18-2.el8ost
  • Red Hat Red Hat OpenStack Services on OpenShift 18.0 0:26.2.5.21-2.el9ost
  • erlang Debian 13 1:27.3.4.1+dfsg-1+deb13u3
  • erlang Debian 14 1:27.3.4.12+dfsg-1

debian advisories DEBIAN-CVE-2026-42790

  • erlang Ubuntu 22.04 LTS 1:24.2.1+dfsg-1ubuntu0.8
  • erlang Ubuntu 24.04 LTS 1:25.3.2.8+dfsg-1ubuntu4.8
  • erlang Ubuntu 26.04 LTS 1:27.3.4.6+dfsg-1ubuntu0.2
  • erlang Ubuntu Pro 18.04 LTS 1:20.2.2+dfsg-1ubuntu2+esm4
  • erlang Ubuntu Pro 20.04 LTS 1:22.2.7+dfsg-1ubuntu0.5+esm3

ubuntu advisories UBUNTU-CVE-2026-42790

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

  • erlang27 hummingbird 1 27.3.4.17-1.hum1
  • erlang27-et hummingbird 1 27.3.4.17-1.hum1
  • erlang27-wx hummingbird 1 27.3.4.17-1.hum1
  • erlang27-ftp hummingbird 1 27.3.4.17-1.hum1
  • erlang27-ssh hummingbird 1 27.3.4.17-1.hum1
  • erlang27-ssl hummingbird 1 27.3.4.17-1.hum1
  • erlang27-asn1 hummingbird 1 27.3.4.17-1.hum1
  • erlang27-edoc hummingbird 1 27.3.4.17-1.hum1

red hat advisories RHSA-2026:63160RHSA-2026:54757RHSA-2026:39809

  • erlang SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 23.3.4.19-150300.3.39.1
  • erlang26 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Server Applications 15 SP7 26.2.1-150300.7.28.1
  • erlang SLES for SAP applications 16.0, SLES 16.0 27.1.3-160000.5.1

suse advisories SUSE-SU-2026:3645-1SUSE-SU-2026:3579-1SUSE-SU-2026:22082-1

  • erlang openSUSE Tumbleweed 28.5.0.4-1.1
  • erlang openSUSE Leap 16.0 27.1.3-160000.5.1
  • erlang27 openSUSE Tumbleweed 27.1.3-2.1

opensuse advisories openSUSE-SU-2026:11559-1openSUSE-SU-2026:20907-1openSUSE-SU-2026:10947-1

  • erlang Azure Linux 3.0 26.2.5.21-1

azure linux advisories AZL-89175

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-2026-42790 updated cvss 7.4

erlang: Erlang OTP public_key: Certificate validation bypass allows hostname spoofing

  • Red Hat OpenStack Platform 17.1 erlang, erlang-ssl, erlang-asn1, erlang-erts, erlang-sasl, erlang-snmp, +14 more
    affected: workaround, no fix available
  • Red Hat Hardened Images erlang27 27.3.4.17-1.hum1, erlang27-et 27.3.4.17-1.hum1, erlang27-wx 27.3.4.17-1.hum1, erlang27-ftp 27.3.4.17-1.hum1, erlang27-ssh 27.3.4.17-1.hum1, erlang27-ssl 27.3.4.17-1.hum1, +33 more
    fixed: vendor fix RHSA-2026:63160
  • Red Hat OpenStack Platform 16.2 erlang 23.3.4.18-2.el8ost, erlang-ssl 23.3.4.18-2.el8ost, erlang-asn1 23.3.4.18-2.el8ost, erlang-erts 23.3.4.18-2.el8ost, erlang-hipe 23.3.4.18-2.el8ost, erlang-sasl 23.3.4.18-2.el8ost, +15 more
    fixed: vendor fix RHSA-2026:54757
  • Red Hat OpenStack Services on OpenShift 18.0 erlang 26.2.5.21-2.el9ost, erlang-ssl 26.2.5.21-2.el9ost, erlang-asn1 26.2.5.21-2.el9ost, erlang-erts 26.2.5.21-2.el9ost, erlang-sasl 26.2.5.21-2.el9ost, erlang-snmp 26.2.5.21-2.el9ost, +14 more
    fixed: vendor fix RHSA-2026:39809
  • Red Hat OpenStack Platform 16.2 etcd 3.3.23-22.el8ost, python-pyasn1 0.4.6-4.el8ost, python3-pyasn1 0.4.6-4.el8ost, collectd-sensubility 0.2.1-1.1.el8ost, python3-pyasn1-modules 0.4.6-4.el8ost, puppet-git 0.5.0-2.20250728140843.4e4498e.el8ost, +60 more
    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
no
Technical impact
total
Assessed
5 mo ago

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 28% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 7.6 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
CISA ADP 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CNA 4.0 7.6 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CNA 3.1 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

  • Erlang OTP
  • Red Hat Red Hat OpenStack Platform 16.2
  • Red Hat Red Hat OpenStack Services on OpenShift 18.0
  • Red Hat Red Hat Hardened Images
  • Red Hat Red Hat OpenStack Platform 17.1

Classification

Weakness
  • CWE-295 Improper Certificate Validation
  • CWE-297 Improper Validation of Certificate with Host Mismatch

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.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.