CVE-2026-42789

HIGH EPSS 14.9%
Published May 27, 20261mo ago · Modified Jun 17, 20261w ago
7.0 CVSS 4.0
High
Find Similar
Published May 27, 2026 1mo ago
Last Modified Jun 17, 2026 1w ago

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.

CVSS Details

Base Score
7.0
Exploitability
—
Impact
—
Vector string
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
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction None
Scope X

Threat Intelligence

EPSS Exploit Probability
14.9% percentile
Exploit & Patch Status
No Known Exploit
Patch Available

Weaknesses 2

CWE-295
CWE-296

Affected Products 4

VendorProductVersionRange
erlangerlang\/otp*≥17.0  –  <26.2.5.21
erlangerlang\/otp*≥27.0  –  <27.3.4.12
erlangerlang\/otp*≥28.0  –  <28.5.0.1
erlangerlang\/otp*≥29.0  –  <29.0.1

References 6

  • cna.erlef.org https://cna.erlef.org/cves/CVE-2026-42789.html
    Third Party Advisory
  • github.com https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db
    Patch
  • github.com https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd
    Patch
  • github.com https://github.com/erlang/otp/security/advisories/GHSA-c99q-jmpx-v8qq
    Vendor Advisory
  • osv.dev https://osv.dev/vulnerability/EEF-CVE-2026-42789
    Third Party Advisory
  • erlang.org https://www.erlang.org/doc/system/versions.html#order-of-versions
    Product

Remediation

  • github.com https://github.com/erlang/otp/commit/471cd2f664300a95353c467873800bbe706005db
    Patch
  • github.com https://github.com/erlang/otp/commit/59c8d824386b2eb1614ff9340624843ef6aca0fd
    Patch