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Erlang OTP CVE-2026-42791

| EUVDEUVD-2026-32273 MEDIUM
Improper Certificate Validation (CWE-295)
2026-05-27 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Authentication Bypass Erlang Otp Red Hat
Medium
Disputed · 6.3 NVD
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Severity by source

Sources disagree (Low–High)
NVD PRIMARY
6.3 MEDIUM
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/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
SUSE
7.4 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Red Hat
5.9 LOW
qualitative

vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.

CVSS VectorNVD

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:L/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
High
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

2
Source Code Evidence Fetched
May 27, 2026 - 22:23 vuln.today
Analysis Generated
May 27, 2026 - 22:23 vuln.today

DescriptionCVE.org

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid.

OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid.

This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case - server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate.

This issue affects OTP from OTP 27.0 before OTP 27.3.4.12, 28.5.0.1, and 29.0.1 corresponding to public_key from 1.16 before 1.17.1.3, 1.20.3.1, and 1.21.1.

AnalysisAI

OCSP responder certificate validity bypass in Erlang OTP's public_key library allows forged OCSP responses-signed with the private key of an expired responder certificate-to be accepted as valid, defeating TLS certificate revocation checks. Affected deployments include TLS clients using OCSP stapling via the ssl application, and any application calling public_key:pkix_ocsp_validate/5 directly for server-side client certificate validation. An attacker who has obtained the private key of an expired CA-designated OCSP responder can present a revoked TLS certificate alongside a forged OCSP response and achieve authentication bypass. No public exploit code exists and CISA KEV does not list this vulnerability; SSVC rates exploitation as none at time of analysis.

Technical ContextAI

The vulnerability resides in lib/public_key/src/pubkey_ocsp.erl, specifically in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3. OCSP (Online Certificate Status Protocol, RFC 6960) is a certificate revocation checking mechanism; when used in TLS via OCSP stapling, the server pre-fetches a signed OCSP response from the CA's responder and presents it to clients during the TLS handshake. RFC 5280 Section 4.1.2.5 mandates that relying parties check the notBefore and notAfter validity fields of all certificates in a chain, including OCSP responder certificates. The root cause (CWE-295: Improper Certificate Validation) is that pubkey_ocsp.erl called neither parse_and_check_validity_dates nor any equivalent time-range check on the responder certificate before accepting its signature as authoritative. The fix, introduced in commit 7995f1fdaee3da569bb810358ce0f546471d169b, exports parse_and_check_validity_dates from pubkey_cert.erl and gates responder authorization on a successful validity-period check; not-yet-valid certificates are similarly rejected. Affected CPE scope covers the otp package from version 1.16 and OTP 27.0 onward until the respective fix releases.

RemediationAI

Vendor-released patches are available: upgrade Erlang OTP to 27.3.4.12, 28.5.0.1, or 29.0.1, which correspond to public_key library versions 1.17.1.3, 1.20.3.1, and 1.21.1 respectively. The fix is confirmed in GitHub commits 7995f1fdaee3da569bb810358ce0f546471d169b and b3870e02405c709a872b01ba6086065620cdfe76; the full advisory is at https://github.com/erlang/otp/security/advisories/GHSA-cjxj-wj6x-3fff. For deployments that cannot immediately patch, the most effective compensating control is to disable OCSP stapling in TLS client configurations-this eliminates the attack surface entirely, at the cost of losing revocation status checks via stapling (clients will fall back to CRL or direct OCSP queries if configured, or may lose revocation checking altogether). Alternatively, operators can audit whether any CA-designated OCSP responder certificates in their PKI trust chain have expired, and revoke or rotate their associated private keys to deny an attacker the prerequisite material. Applications using public_key:pkix_ocsp_validate/5 directly for client certificate validation should be temporarily disabled or bypassed to prevent authentication bypass until patching is complete.

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Vendor StatusVendor

SUSE

Severity: High
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Module for Server Applications 15 SP7 Fixed
SUSE Linux Enterprise Server 15 SP7 Fixed

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CVE-2026-42791 vulnerability details – vuln.today
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