CVE-2026-42790
Description
A flaw was found in Erlang OTP public_key. This improper certificate validation vulnerability allows a subordinate Certificate Authority (CA) with restricted DNS nameConstraints to bypass these restrictions. By issuing a leaf certificate that lacks a Subject Alternative Name (SAN) but contains a crafted CommonName (CN), an attacker can trick an Erlang OTP TLS client into accepting it as valid for an out-of-scope hostname. This can lead to hostname spoofing and potential man-in-the-middle attacks, compromising the integrity and confidentiality of communications.
Statement
This Important flaw in Erlang OTP's public_key module allows a subordinate Certificate Authority to bypass DNS name constraints during TLS hostname verification. An attacker could exploit this by issuing a specially crafted certificate lacking a Subject Alternative Name but containing a malicious CommonName, enabling hostname spoofing and potential man-in-the-middle attacks against Red Hat products acting as Erlang OTP TLS clients.
Mitigation
Ensure all TLS certificates used in the deployment include Subject Alternative Name (SAN) extensions with the appropriate DNS entries. Certificates relying solely on the CommonName (CN) field for hostname identification are susceptible to this bypass. For Erlang applications, the verify_fun option in the ssl module can be configured to reject peer certificates missing the subjectAltName extension.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.4 | 8.1 | 7.4 |
| Attack Vector | Network | Network | Network |
| Attack Complexity | High | Low | High |
| Privileges Required | None | None | None |
| User Interaction | None | Required | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | High | High | High |
| Integrity Impact | High | High | High |
| Availability Impact | None | None | None |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
cve.org: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Integrity,Authentication
Technical Impact: Bypass Protection Mechanism; Gain Privileges or Assume Identity
When a certificate is invalid or malicious, it might allow an attacker to spoof a trusted entity by interfering in the communication path between the host and client. The product might connect to a malicious host while believing it is a trusted host, or the product might be deceived into accepting spoofed data that appears to originate from a trusted host.
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