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Erlang Otp CVE-2026-42789

| EUVDEUVD-2026-32272 HIGH
Improper Certificate Validation (CWE-295)
2026-05-27 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Authentication Bypass Erlang Otp Erlang
7.0
CVSS 4.0 · Vendor: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
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Vulnerability Assessment

Weakness
CWE
CWE-295
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V12 - Secure Communication Certificate validation
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.0% exploitation probability (EPSS)

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AnalysisAIv1 – May 27, 2026

Certificate chain forgery in Erlang/OTP's public_key application (pubkey_cert module) lets a non-CA end-entity certificate act as an intermediate issuer, allowing an attacker holding such a certificate's private key to sign forged leaf certificates for arbitrary identities that public_key:pkix_path_validation/3 will accept. This breaks server identity verification for TLS clients and client-certificate verification for mTLS servers across any application using the OTP ssl stack with the default verifier. Tracked as CWE-295 with a CVSS 4.0 base score of 7.0 (subsequent-system confidentiality and integrity rated High); no public exploit identified at time of analysis and it is not listed in CISA KEV, with the only available code being the vendor fix commits.

Affected VersionsENISA

otp 17.0 <*
otp 84adefa331c4159d432d22840663c38f155cd4c1 <*
otp 0.22 <*

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Severity by source

Vendor (6b3ad84c-e1a6-4bf7-a703-f496b71e49db) PRIMARY 7.0 HIGH
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:H/SI:H/SA:N
SUSE 7.4 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat 8.0 HIGH

Primary rating from Vendor (6b3ad84c-e1a6-4bf7-a703-f496b71e49db).

CVSS VectorVendor: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
Present
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
Low
Vulnerable system: Integrity
Low
Vulnerable system: Availability
None
Subsequent system: Confidentiality
High
Subsequent system: Integrity
High
Subsequent system: Availability
None

DescriptionCVE.org

Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery.

In lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain passed to public_key:pkix_path_validation/3: the cA:false clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the keyUsage check only fires when the extension is present, so a certificate lacking keyUsage entirely bypasses the keyCertSign enforcement.

Any party holding an end-entity certificate with basicConstraints cA:false and no keyUsage extension, issued by any CA in the victim's trust store, can use that certificate's private key to sign forged leaf certificates for arbitrary identities. public_key:pkix_path_validation/3 accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP ssl application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers.

This issue affects OTP from OTP 17.0 before OTP 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 0.22 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.

Executive ViewAI

Why It Matters

Erlang/OTP's public_key application contains a certificate chain forgery vulnerability (CVSS 7.0) allowing attackers with a compromised certificate's private key to create forged certificates that the standard TLS verifier will accept as legitimate. This breaks server identity verification for all TLS clients and client authentication for mTLS servers across the entire Erlang ecosystem using default verification settings. Organizations must immediately identify systems at risk and implement interim controls, as no vendor-released patch is currently available.

Recommended Action

Within 24 hours: Inventory all Erlang/OTP deployments using the public_key and ssl modules; document versions and deployment scope. Within 7 days: Implement certificate pinning or custom validation layers for critical TLS connections; restrict certificate issuance authority and monitor certificate creation events; evaluate whether vendor fix commits (available in Erlang/OTP source repositories) can be applied to custom builds. Within 30 days: Establish organization-wide monitoring for anomalous certificate validation events; coordinate upgrade strategy with Erlang/OTP release cycle for official patched versions; test mitigations in production-adjacent environments.

Business Impact: High
Compensating Controls

No vendor-released patch identified at time of analysis. Interim mitigations: implement certificate pinning for critical connections; apply additional certificate chain validation beyond the default verifier; restrict administrative access to certificate issuance systems; enable audit logging of all certificate validation events; consider disabling unnecessary TLS connections pending patch availability. Organizations with source build capabilities may apply vendor fix commits directly.

Threat Intelligence Overview

EPSS Score
0.0%
Top 92% exploitable
Data Quality
8 sources
Confidence: High
EUVD NVD CVE.org EPSS Vulnrichment MSRC Vendor GitHub VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.0%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Scheduled
Exploitation
None
System Exposure· derived
Open
Automatable
No
Human Impact
High
Technical Impact
Partial

Priority Score

35
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +35
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

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Same weakness CWE-295 – Improper Certificate Validation

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CVE-2026-85102 CRITICAL POC
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CVE-2025-68121 CRITICAL POC
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CVE-2025-29331 CRITICAL POC
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CVE-2025-32878 CRITICAL POC
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Same technique Authentication Bypass

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CVE-2023-22515 CRITICAL POC
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CVE-2012-4681 CRITICAL POC
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CVE-2013-2465 CRITICAL POC
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CVE-2011-3544 CRITICAL POC
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CVE-2022-40684 CRITICAL POC
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CVE-2025-61882 CRITICAL POC
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CVE-2024-0012 CRITICAL POC
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Vendor StatusVendor

SUSE

Severity: High
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Server 15 SP7 Fixed

References

Advisories & patches
ADVISORY https://vuldb.com/vuln/366392 REF https://access.redhat.com/errata/RHSA-2026:39809 REF https://access.redhat.com/errata/RHSA-2026:54757 REF https://access.redhat.com/security/cve/CVE-2026-42789 REF https://bugzilla.redhat.com/show_bug.cgi?id=2482093 REF https://cna.erlef.org/cves/CVE-2026-42789.html REF https://github.com/erlang/otp/commit/0a05b7ca33fb0b3f0a6cb9ae34252bb3a74032b8 REF https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db REF https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd REF https://github.com/erlang/otp/commit/75ca4c0dc2bbdb286ac3c3fe89cb4b4d2b4dc333 REF https://github.com/erlang/otp/commit/82af606b5437c4de1276dbcc8855a47e88231226 REF https://github.com/erlang/otp/security/advisories/GHSA-c99q-jmpx-v8qq REF https://osv.dev/vulnerability/EEF-CVE-2026-42789 REF https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-42789.json REF https://www.erlang.org/doc/system/versions.html#order-of-versions

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