# CVE-2026-42790: Erlang OTP certificate validation bypass in public_key module

Source: https://junglewise.ai/threats/cve-2026-42790-erlang-otp-certificate-validation-bypass-in-public-key-module  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-27. Updated: 2026-05-27  
License: CC BY 4.0 with a link back

CVE-2026-42790 · Severity: info · CVSS 7.6 · Published 2026-05-27

Erlang OTP is a popular development platform used to build scalable, high-availability systems. A flaw in its security library allows a restricted certificate authority to issue fraudulent certificates that appear valid to Erlang-based applications. An attacker could use this to impersonate legitimate websites or services, potentially leading to intercepted communications or the theft of sensitive data.

Technologies: [Erlang OTP](https://junglewise.ai/threats/technologies/otp), [Erlang Public Key](https://junglewise.ai/threats/technologies/public-key). Vendors: [Erlang](https://junglewise.ai/threats/vendors/erlang).

## Quick answers

**Is CVE-2026-42790 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42790 being exploited in the wild.

**How severe is CVE-2026-42790?** Informational severity, with a CVSS score of 7.6, published 27 May 2026.

**Which products and versions are affected?** Erlang OTP 19.3 before 26.2.5.21, 27.3.4.12, 28.5.0.1, 29.0.1; Erlang Public Key 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, 1.21.1.

**Is there a fix for CVE-2026-42790?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-42790 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-42790?** Check whether you run Erlang OTP or Erlang Public Key at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in the Erlang OTP public_key library (specifically the pubkey_cert and public_key modules) where two flaws combine to bypass DNS nameConstraints. First, pubkey_cert:validate_names/6 only validates Subject Alternative Name (SAN) entries against nameConstraints; a certificate without a SAN extension bypasses these checks entirely. Second, public_key:pkix_verify_hostname/3 incorrectly falls back to the subject CommonName (CN) when no SAN is present, even when using strict HTTPS matching. An attacker with a subordinate CA restricted by DNS nameConstraints can issue a CN-only leaf certificate for an out-of-scope domain that an OTP TLS client will trust. This affects stock ssl:connect configurations using verify_peer and the canonical HTTPS hostname matcher.

## Affected products

- Erlang OTP 19.3 before 26.2.5.21, 27.3.4.12, 28.5.0.1, 29.0.1
- Erlang public_key 1.4 before 1.15.1.7, 1.17.1.3, 1.20.3.1, 1.21.1

## Timeline

- 2026-05-05: other: Fixes authored in Erlang OTP repository
- 2026-05-27: advisory: CVE-2026-42790 published by Erlang Ecosystem Foundation

## References

- [https://cna.erlef.org/cves/CVE-2026-42790.html](https://cna.erlef.org/cves/CVE-2026-42790.html)
- [https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759](https://github.com/erlang/otp/commit/0769050c69d73762672b0db1347b6993a5b31759)
- [https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a](https://github.com/erlang/otp/commit/21abed64eb2026b5f82f432709e4e932f9be389a)
- [https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457](https://github.com/erlang/otp/commit/fb67c6d1836f51105a96d8b769e71e4215a79457)
- [https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447](https://github.com/erlang/otp/security/advisories/GHSA-22cw-4ph4-6447)
- [https://www.erlang.org/doc/system/versions.html](https://www.erlang.org/doc/system/versions.html)

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