HighCVE-2026-42790

    nameConstraints DNS bypass via subject CommonName fallback in public_key hostname verification (CVE-2026-42790)

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

    What is affected, what to do

    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.

    Update erlang\/otp to version 27.3.4.12, Erlang/OTP to version 1.15.1.7.

    Affected
    • Erlang OTP gte 1.4..*
    • Erlang OTP gte 19.3..*

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    Metrics

    8.1

    Priority

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

    Source: NVD, CVSS v3

    8.1

    CVSS v3

    Severity High on the scale from 0 to 10.

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

    0.3 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 28.1

    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
    64.80 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
    8.1 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
    8.1
    CVSS v4

    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
    7.6
    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
    0.3 %
    Low — model estimates < 1% 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
    28.1
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    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
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 27 May 2026
    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-295, CWE-297, CWE-295

    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

    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.

    Source: redhat_csaf, suse_csaf, Debian Security Advisories, BSI WID Portal, BSI CSAF, NVD (NIST), ENISA EUVD, CVE.org (MITRE), Microsoft Security Update Guide, cvelistv5, OSV (Open Source Vulnerabilities)

    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
    ErlangOTP
    • ≥ 19.3
    • ≥ 1.4
    • —
    • —
    erlangerlang\/otp
    • 27.0 – < 27.3.4.12
    • 28.0 – < 28.5.0.1
    • 29.0 – < 29.0.1
    • 19.3 – < 26.2.5.21
    • 27.3.4.12
    • 28.5.0.1
    • 29.0.1
    • 26.2.5.21
    Open SourceErlang/OTP
    • < 1.15.1.7
    • < 26.2.5.21
    • < 28.5.0.1
    • < 1.20.3.1
    • < 27.3.4.12
    • < 29.0.1
    • < 1.17.1.3
    • < 1.21.1
    • 1.15.1.7
    • 26.2.5.21
    • 28.5.0.1
    • 1.20.3.1
    • 27.3.4.12
    • 29.0.1
    • 1.17.1.3
    • 1.21.1

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianerlangtrixie

    Weakness classes (CWE)

    • CWE-295Improper Certificate Validation

      Base

      The product does not validate, or incorrectly validates, a certificate.

      Entry at MITRE CWE-295

    • CWE-297Improper Validation of Certificate with Host Mismatch

      Variant

      The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.

      Entry at MITRE CWE-297

    • CWE-295Improper Certificate Validation

      Base

      The product does not validate, or incorrectly validates, a certificate.

      Entry at MITRE CWE-295

    References & sources

    • github.comerlang/otp/security/advisories/GHSA-22cw-4ph4-6447advisory, Vendor advisory, related, Vendor advisory
    • cna.erlef.orgcves/CVE-2026-42790.htmlweb, related, Third-party advisory
    • erlang.orgdoc/system/versions.htmlweb, x_version-scheme, Product
    • github.comerlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759fix, Patch, Patch
    • github.comerlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457fix, Patch, Patch
    • github.comerlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389afix, Patch, Patch
    • OSV (Open Source Vulnerabilities)vulnerability/EEF-CVE-2026-42790related, Mitigation, Third-party advisory
    • access.redhat.comsecurity/cve/CVE-2026-42790Vulnerability database, x_refsource_REDHAT
    • bugzilla.redhat.comRHBZ#2482286Issue tracking, x_refsource_REDHAT
    • security.access.redhat.comdata/csaf/v2/vex/2026/cve-2026-42790.jsonx_sadp-csaf-vex
    • access.redhat.comerrata/RHSA-2026:54757Vendor advisory, x_refsource_REDHAT
    • access.redhat.comerrata/RHSA-2026:39809Vendor advisory, x_refsource_REDHAT

    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. Record modifiedEEF

      Show 21 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-42790.html
      Referenceadded
      —
      https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759
      Referenceadded
      —
      https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a
      Referenceadded
      —
      https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457
      Referenceadded
      —
      https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-42790
      Referenceadded
      —
      https://www.erlang.org/doc/system/versions.html#order-of-versions
      Referenceremoved
      https://cna.erlef.org/cves/CVE-2026-42790.html
      —
      Referenceremoved
      https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759
      —
      Referenceremoved
      https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a
      —
      Referenceremoved
      https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457
      —
      Referenceremoved
      https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447
      —
      Referenceremoved
      https://osv.dev/vulnerability/EEF-CVE-2026-42790
      —
      Referenceremoved
      https://www.erlang.org/doc/system/versions.html#order-of-versions
      —
      Reference typeremoved
      https://cna.erlef.org/cves/CVE-2026-42790.html Types: Third Party Advisory
      —
      Reference typeremoved
      https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759 Types: Patch
      —
      Reference typeremoved
      https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a Types: Patch
      —
      Reference typeremoved
      https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457 Types: Patch
      —
      Reference typeremoved
      https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447 Types: Vendor Advisory
      —
      Reference typeremoved
      https://osv.dev/vulnerability/EEF-CVE-2026-42790 Types: Mitigation, Third Party Advisory
      —
      Reference typeremoved
      https://www.erlang.org/doc/system/versions.html#order-of-versions Types: Product
      —

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

    2. Record modifiedRed Hat ADP

      Show 11 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/42xxx/CVE-2026-42790.json">CVE-2026-42790</a>
      Referenceadded
      —
      https://access.redhat.com/errata/RHSA-2026:39809
      Referenceadded
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      https://access.redhat.com/errata/RHSA-2026:54757
      Referenceadded
      —
      https://access.redhat.com/security/cve/CVE-2026-42790
      Referenceadded
      —
      https://bugzilla.redhat.com/show_bug.cgi?id=2482286
      Referenceadded
      —
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42790.json
      Referenceremoved
      https://access.redhat.com/errata/RHSA-2026:39809
      —
      Referenceremoved
      https://access.redhat.com/errata/RHSA-2026:54757
      —
      Referenceremoved
      https://access.redhat.com/security/cve/CVE-2026-42790
      —
      Referenceremoved
      https://bugzilla.redhat.com/show_bug.cgi?id=2482286
      —
      Referenceremoved
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42790.json
      —

      Source identifier: 0b0ca135-0b70-47e7-9f44-1890c2a1c46c

    3. Record modifiedEEF

      Description added or changed

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionchanged
      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 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.
      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.

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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