CVE-2026-42790

Publication date 27 May 2026

Last updated 8 October 2026

Ubuntu priority

Medium

Why this priority?

Cvss 3 Severity Score

7.4 · High

Score breakdown

Description

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.

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
Not affected
14.04 LTS trusty
Not affected

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Severity score breakdown

CVSS version:

Base score 7.6 · High

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

Base score 7.4 · High

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

References

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