CVE-2026-42790

unknown

Published 2026-05-27 · Modified 2026-05-28

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CVSS v3

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CVSS v4 NEW

7.6

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

VIR risk

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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 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.

Predictions

Exploit likelihood

20%

Patch ETA

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Heuristic predictions, AS-IS, for prioritization only.

Mitigations

Mitigation details

Source: Debian Security Tracker · View original ↗ · DFSG

CVE-2026-42790 NameCVE-2026-42790 DescriptionImproper 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…

CVE-2026-42790

Name	CVE-2026-42790
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 26.2.5.21, 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, and 1.21.1.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
erlang (PTS)	bullseye	1:23.2.6+dfsg-1+deb11u1	vulnerable
	bullseye (security)	1:23.2.6+dfsg-1+deb11u4	vulnerable
	bookworm	1:25.2.3+dfsg-1+deb12u4	vulnerable
	bookworm (security)	1:25.2.3+dfsg-1+deb12u1	vulnerable
	trixie	1:27.3.4.1+dfsg-1+deb13u2	vulnerable
	forky	1:27.3.4.11+dfsg-7	vulnerable
	sid	1:27.3.4.12+dfsg-1	fixed

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
erlang	source	(unstable)	1:27.3.4.12+dfsg-1

Notes

https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447
https://cna.erlef.org/cves/CVE-2026-42790.html
https://osv.dev/vulnerability/EEF-CVE-2026-42790
https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759 (OTP-26.2.5.21)
https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457 (OTP-27.3.4.12)
https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a (OTP-29.0.1, OTP-28.5.0.1)

Home - Debian Security - Source (Git)

Apply commands

text fix

Notes

https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447https://cna.erlef.org/cves/CVE-2026-42790.htmlhttps://osv.dev/vulnerability/EEF-CVE-2026-42790https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759 (OTP-26.2.5.21)https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457 (OTP-27.3.4.12)https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a (OTP-29.0.1, OTP-28.5.0.1)

OS impact

OS	Version	Status	Fixed in
sles		affected
debian	bookworm	affected
debian	bullseye	affected
debian	forky	affected
debian	sid	fixed	`1:27.3.4.12+dfsg-1`
debian	trixie	affected

References

CWEs

CWE-295 CWE-297

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.