CVE-2026-42789

Publication date 27 May 2026

Last updated 8 October 2026

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

8.0 · High

Score breakdown

Description

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, OTP 27.3.4.12, OTP 28.5.0.1, and OTP 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. Whether OTP before OTP 17.0, corresponding to public_key before 0.22, is affected is unknown.

Status

Package Ubuntu Release Status
erlang 26.04 LTS resolute
Fixed 1:27.3.4.6+dfsg-1ubuntu0.2
25.10 questing Ignored end of life, was needs-triage
24.04 LTS noble
Fixed 1:25.3.2.8+dfsg-1ubuntu4.8
22.04 LTS jammy
Fixed 1:24.2.1+dfsg-1ubuntu0.8
20.04 LTS focal
Fixed 1:22.2.7+dfsg-1ubuntu0.5+esm3
18.04 LTS bionic
Fixed 1:20.2.2+dfsg-1ubuntu2+esm4
16.04 LTS xenial
Fixed 1:18.3-dfsg-1ubuntu3.1+esm4
14.04 LTS trusty
Fixed 1:16.b.3-dfsg-1ubuntu2.2+esm3

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Severity score breakdown

CVSS version:

Base score 7.0 · High

Vector: 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

Base score 8.0 · High

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:H/A:N

References

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