CVE-2026-42789

unknown

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

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CVSS v3

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CVSS v4 NEW

7.0

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/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 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.

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-2026-42789 NameCVE-2026-42789 DescriptionImproper 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…

CVE-2026-42789

Name	CVE-2026-42789
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, 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.
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, sid	1:27.3.4.11+dfsg-7	vulnerable

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-c99q-jmpx-v8qq
https://cna.erlef.org/cves/CVE-2026-42789.html
https://osv.dev/vulnerability/EEF-CVE-2026-42789
https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db (OTP-26.2.5.21)
https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd (OTP-29.0.1, OTP-28.5.0.1, OTP-27.3.4.12)

Home - Debian Security - Source (Git)

Apply commands

text fix

Notes

https://github.com/erlang/otp/security/advisories/GHSA-c99q-jmpx-v8qqhttps://cna.erlef.org/cves/CVE-2026-42789.htmlhttps://osv.dev/vulnerability/EEF-CVE-2026-42789https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db (OTP-26.2.5.21)https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd (OTP-29.0.1, OTP-28.5.0.1, OTP-27.3.4.12)

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-296

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

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