CVE-2026-42789Network attack vector

Certificate chain forgery via non-CA intermediate acceptance

Published May 27, 2026 · Updated May 27, 2026

Improper certificate-chain validation in Erlang/OTP allows remote attackers to forge trusted TLS identities via crafted certificate chains. pubkey_cert:validate_extensions/7 continues after basicConstraints cA:false and enforces keyCertSign only when keyUsage exists, so issuer-position end-entity certificates pass. Exploitation requires the matching private key for such a certificate issued by a CA in the target trust store; accepted chains can impersonate TLS servers or mTLS clients.

CVSS severity7.0
High
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper certificate-chain validation in Erlang/OTP allows remote attackers to forge trusted TLS identities via crafted certificate chains. pubkey_cert:validate_extensions/7 continues after basicConstraints cA:false and enforces keyCertSign only when keyUsage exists, so issuer-position end-entity certificates pass. Exploitation requires the matching private key for such a certificate issued by a CA in the target trust store; accepted chains can impersonate TLS servers or mTLS clients.

The record

CVE
CVE-2026-42789
Published
May 27, 2026
Updated
May 27, 2026
Vendor
Erlang
Product
Erlang/OTP
Classifications
CWE-296, CWE-295, CAPEC-475, T1587.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 27, 2026CVE publishedPublication date reported by the CVE source.
  2. May 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.22 <* changes=[{"at":"1.15.1.7","status":"unaffected"},{"at":"1.17.1.3","status":"unaffected"},{"at":"1.20.3.1","status":"unaffected"},{"at":"1.21.1","status":"unaffected"}]
  2. Affected versionversion=17.0 <* changes=[{"at":"26.2.5.21","status":"unaffected"},{"at":"27.3.4.12","status":"unaffected"},{"at":"28.5.0.1","status":"unaffected"},{"at":"29.0.1","status":"unaffected"}]
  3. Affected versionversion=84adefa331c4159d432d22840663c38f155cd4c1 <* changes=[{"at":"471cd2f664300a95353c467873800bbe706005db","status":"unaffected"},{"at":"59c8d824386b2eb1614ff9340624843ef6aca0fd","status":"unaffected"}]

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Erlang · Erlang/OTPversion=0.22 <* changes=[{"at":"1.15.1.7","status":"unaffected"},{"at":"1.17.1.3","status":"unaffected"},{"at":"1.20.3.1","status":"unaffected"},{"at":"1.21.1","status":"unaffected"}]; version=17.0 <* changes=[{"at":"26.2.5.21","status":"unaffected"},{"at":"27.3.4.12","status":"unaffected"},{"at":"28.5.0.1","status":"unaffected"},{"at":"29.0.1","status":"unaffected"}]; version=84adefa331c4159d432d22840663c38f155cd4c1 <* changes=[{"at":"471cd2f664300a95353c467873800bbe706005db","status":"unaffected"},{"at":"59c8d824386b2eb1614ff9340624843ef6aca0fd","status":"unaffected"}]

Published CVSS scores

4.8NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
8.0Red HatCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N
7.0Erlang Ecosystem FoundationCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:H/SI:H/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-296Improper Following of a Certificate's Chain of Trust
CWE-295Improper Certificate Validation
CAPEC-475Signature Spoofing by Improper Validation
T1587.003Develop Capabilities: Digital Certificates

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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