CVE-2026-42789 | Vulnerability Intelligence

Stored catalog record

Source record retrieved 2026-10-28T10:25:17.313581+00:00. Scheduled imports handle updates; this page does not assert that the provider was queried just now.

Vulnerability overview

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 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to public_key from 0.22 before 1.17.1.7, 1.20.3.6, and 1.21.8. Whether OTP before OTP 17.0, corresponding to public_key before 0.22, is affected is unknown.

Patch review priority

Assess exposure and vendor guidance

No higher-priority signal is available in the current stored evidence.

FIRST EPSS: 0.38% · percentile 32.1 · score date 2026-10-27.

EPSS estimates probability of exploitation in the next 30 days. It does not measure your exposure or prove exploitation. The elevated threshold is 10%; CISA KEV takes precedence. About FIRST EPSS ↗

Severity and scoring

CVSS score: 7.0 · HIGH
CVSS version: 4.0
CVSS 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/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
Weaknesses: CWE-295, CWE-296

CVSS measures technical severity; it does not establish whether this vulnerability is being exploited in your environment.

Known exploitation and remediation

Not listed in the CISA catalog retrieved for this record. This does not establish that exploitation has not occurred.

Verify affected versions and patch availability in the vendor advisory before making changes.

Affected products and versions

cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
From (inclusive): 17.0
Before (exclusive): 26.2.5.21
cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
From (inclusive): 27.0
Before (exclusive): 27.3.4.12
cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
From (inclusive): 28.0
Before (exclusive): 28.5.0.1
cpe:2.3:a:erlang:erlang\/otp:*:*:*:*:*:*:*:*
From (inclusive): 29.0
Before (exclusive): 29.0.1

These are NVD CPE applicability entries. Some products depend on configuration conditions; consult the official record to confirm applicability.

Advisories and references

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