Erlang OTP prior 29.0.1 TLS Endpoint pubkey_cert.erl certificate validation

CVSS Meta Temp Score
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CTI Interest Score
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4.2$0-$5k0.00

Summaryinfo

A vulnerability described as problematic has been identified in Erlang OTP. This issue affects some unknown processing in the library lib/public_key/src/pubkey_cert.erl of the component TLS Endpoint. Such manipulation leads to certificate validation. This vulnerability is uniquely identified as CVE-2026-42789. The attack can be launched remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Erlang OTP. Affected by this issue is an unknown code block in the library lib/public_key/src/pubkey_cert.erl of the component TLS Endpoint. The manipulation with an unknown input leads to a certificate validation vulnerability. Using CWE to declare the problem leads to CWE-295. The product does not validate, or incorrectly validates, a certificate. Impacted is integrity. CVE summarizes:

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.

The weakness was disclosed by John Downey and Jakub Witczak as GHSA-c99q-jmpx-v8qq. The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-42789 since 04/29/2026. The exploitation is known to be difficult. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1587.003.

Upgrading to version 0.22, 1.15.1.7, 1.17.1.3, 1.20.3.1, 1.21.1, 17.0, 26.2.5.21, 27.3.4.12, 28.5.0.1 or 29.0.1 eliminates this vulnerability. Applying the patch 471cd2f664300a95353c467873800bbe706005db is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Vendor

Name

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔒
CNA CVSS-BT Score: 🔒
CNA Vector: 🔒

CVSSv3info

VulDB Meta Base Score: 4.2
VulDB Meta Temp Score: 4.2

VulDB Base Score: 3.7
VulDB Temp Score: 3.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

NVD Base Score: 4.8
NVD Vector: 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Certificate validation
CWE: CWE-295 / CWE-287
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: OTP 0.22/1.15.1.7/1.17.1.3/1.20.3.1/1.21.1/17.0/26.2.5.21/27.3.4.12/28.5.0.1/29.0.1
Patch: 471cd2f664300a95353c467873800bbe706005db

Timelineinfo

04/29/2026 CVE reserved
05/27/2026 +28 days Advisory disclosed
05/27/2026 +0 days VulDB entry created
06/07/2026 +10 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: GHSA-c99q-jmpx-v8qq
Researcher: John Downey, Jakub Witczak
Status: Confirmed

CVE: CVE-2026-42789 (🔒)
GCVE (CVE): GCVE-0-2026-42789
GCVE (VulDB): GCVE-100-366392

Entryinfo

Created: 05/27/2026 18:53
Updated: 06/07/2026 01:15
Changes: 05/27/2026 18:53 (71), 06/07/2026 01:15 (11)
Complete: 🔍
Cache ID: 216::103

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