Is CVE-2026-42789 being actively exploited?

It is not currently in CISA's KEV catalog. Its EPSS exploitation probability is 0%.

What products does CVE-2026-42789 affect?

Tracked products affected include Erlang/OTP. Check the version you run to see whether it is affected.

How do I fix CVE-2026-42789?

Apply the vendor fix in your normal patch cycle. An official patch or advisory is available. Upgrade affected products to a fixed version.

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CVE-2026-42789

Q: What is CVE-2026-42789?

CVE-2026-42789 is a medium-severity software vulnerability (CWE-295) with a CVSS score of 4.8. 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/sr

MEDIUM severity · CVSS 4.8 · CWE-295

4.8CVSS MEDIUM

Summary

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.

Impact & exploitability

Attack vectorNetwork

Attack complexityHigh

Privileges requiredNone

User interactionNone

Confidentiality impactLow

Integrity impactLow

Availability impactNone

Exploit probability (EPSS)0%

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

Affected products we track (1)

Erlang/OTP

Recommendation

Apply the vendor fix in your normal patch cycle. Open any affected product above for its exact safe version.

Official patch: https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db ↗

CVE-2026-42789

Summary

Impact & exploitability

Affected products we track (1)

Recommendation

Additional information