CVE-2026-42791
Description
A flaw was found in Erlang OTP's public_key application, specifically in the Online Certificate Status Protocol (OCSP) response verification. A remote attacker who has obtained the private key of an expired Certificate Authority (CA)-designated OCSP responder certificate can forge OCSP responses. This allows a malicious server to present a revoked Transport Layer Security (TLS) certificate, which a client would then accept as valid, leading to an authentication bypass. This vulnerability can also affect applications directly using the public_key:pkix_ocsp_validate/5 API, potentially enabling authentication bypass with revoked client certificates.
Statement
Red Hat rates this flaw as Low rather than Important because exploitation requires the attacker to possess the private key of an expired CA-designated OCSP responder certificate, and the affected OCSP stapling feature is not enabled by default in the Erlang ssl application. The direct impact is limited to integrity — a forged OCSP response is accepted, allowing a revoked certificate to appear valid.
Mitigation
For TLS clients using the Erlang ssl application, disable OCSP stapling by setting {stapling, no_staple} in the client options, or switch to CRL-based revocation checking with {crl_check, true}.
For applications calling public_key:pkix_ocsp_validate/5 directly, validate the responder certificate's validity period in application code before calling the function.
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).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 3.7 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | High | Low | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/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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