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CVE Record

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

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.

HighCVSS 7.6Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

Erlang/OTP TLS clients may trust a certificate for the wrong hostname when a DNS-restricted subordinate CA issues a certificate containing only a CommonName. This can undermine server identity checks and expose intercepted connections to data theft or modification. The flaw is rated high severity, but exploitation requires several specific certificate and connection conditions.

Executive priority

Prioritize remediation for Internet-facing or sensitive services whose OTP clients trust constrained subordinate CAs. The potential impact includes credential, session, or business-data interception and modification. Treat this as a high-priority upgrade, while recognizing that the documented prerequisites make broad opportunistic exploitation less likely than targeted abuse.

Technical view

Two validation behaviors combine: DNS name constraints check subjectAltName entries but do not constrain a CN-only certificate, while public_key hostname verification falls back to CommonName when no subjectAltName exists. Consequently, path validation can accept the certificate and hostname verification can match its out-of-scope CommonName. Stock ssl:connect configurations using verify_peer and the strict HTTPS matcher are reachable.

Likely exposure

Exposure exists where affected Erlang/OTP versions make outbound TLS connections, perform peer and hostname verification, and trust DNS-constrained subordinate CAs. Applications are particularly relevant if they depend on name constraints to limit those CAs. Systems not using OTP TLS clients or not trusting constrained intermediates are less likely exposed, but inventory evidence is required.

Exploitation context

No active exploitation is established: the source bundle marks this CVE absent from KEV and provides no cited exploitation report. Abuse requires a trusted, DNS-constrained subordinate CA, a CN-only leaf certificate naming an unauthorized host, and a connection scenario involving that certificate. CVSS 4.0 rates it 7.6 with high confidentiality and integrity impact.

Researcher notes

Affected scope is stated as OTP 19.3 through versions preceding the listed fixed releases, corresponding to public_key versions before the listed branch fixes. The bundle includes vendor patches but does not establish exploit availability or exploitation in the wild. Validate branch-specific applicability carefully because the supplied affected-package metadata is less precise than the narrative version statement.

Mitigation direction

  • Upgrade to the applicable fixed OTP release: 29.0.1, 28.5.0.1, 27.3.4.12, or 26.2.5.21.
  • Alternatively, update public_key to the corresponding fixed version: 1.21.1, 1.20.3.1, 1.17.1.3, or 1.15.1.7.
  • For older or unclear branches, obtain the supported upgrade path from Erlang/OTP vendor guidance.
  • Review trusted subordinate CAs and reduce unnecessary trust, prioritizing intermediates with DNS name constraints.

Validation and detection

  • Inventory Erlang/OTP and public_key versions in applications that initiate TLS connections.
  • Confirm whether applications use ssl:connect with verify_peer and hostname verification.
  • Inspect relevant trust stores for subordinate CAs carrying permitted or excluded DNS name constraints.
  • Verify deployed versions meet an applicable fixed release threshold after remediation.
  • Regression-test rejection of CN-only certificates naming hosts outside a trusted intermediate's permitted DNS subtree.
Prepared
Confidence
high
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-295: Exact CWE lookup

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cwe · low confidence lookup

CWE-297: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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cve · low confidence lookup

CVE-2026-42790 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.6 (4.0)
Known Exploited
No
Published

Vector: 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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
12Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.6CVSS 4.0HighCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N——EEF
7.4CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N2.25.2redhat-SADP

Vulnerability scoring details

Base CVSS 4.0 score

7.6High
CVSS 4.0 vector shape for CVE-2026-42790Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: 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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPerlang: Erlang OTP public_key: Certificate validation bypass allows hostname spoofing
other:Red Hat severity ratingcvssV3_1
  • 2026-05-27T17:02:53.354Z: Reported to Red Hat.
  • 2026-05-27T15:09:01.860Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
ErlangOTPpublic_key, 1.4unknown
ErlangOTPerlang/otp, 19.3, b0c245e8132bb13171e277b1af59c0cec00c9459unknown
Weakness

CWE details

CWE-295CWE-297

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-295 · source CWE mapping

Improper Certificate Validation

Improper Certificate Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-297 · source CWE mapping

Improper Validation of Certificate with Host Mismatch

Improper Validation of Certificate with Host Mismatch represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs