What is the CVSS score of CVE-2026-34457?

CVE-2026-34457 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.1%.

Which versions of Nginx are affected by CVE-2026-34457?

OAuth2 Proxy versions before 7.15.2 contain a critical authentication bypass vulnerability that allows unauthenticated remote attackers to directly access protected resources in deployments using…. A patch is available.

How to fix or mitigate CVE-2026-34457?

Within 24 hours: Identify all deployments of OAuth2 Proxy and determine which instances use nginx auth_request with health check features (--ping-user-agent or --gcp-healthchecks flags enabled). Within 7 days: Upgrade all affected OAuth2 Proxy instances to version 7.15.2 or later. Within 30 days: Conduct access log review for the past 90 days to identify any suspicious health check User-Agent patterns that may indicate exploitation attempts.

Nginx CVE-2026-34457

EUVD-2026-22761 CRITICAL

Authentication Bypass by Spoofing (CWE-290)

2026-04-14 GitHub_M

GHSA-5hvv-m4w4-gf6v

Authentication Bypass Nginx

9.1

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Re-analysis Queued

Apr 17, 2026 - 15:52 vuln.today

cvss_changed

Patch released

Apr 15, 2026 - 02:30 nvd

Patch available

Analysis Generated

Apr 15, 2026 - 01:08 vuln.today

EUVD ID Assigned

Apr 14, 2026 - 22:46 euvd

EUVD-2026-22761

Analysis Generated

Apr 14, 2026 - 22:46 vuln.today

CVE Published

Apr 14, 2026 - 22:14 nvd

CRITICAL 9.1

DescriptionGitHub Advisory

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions prior to 7.15.2 contain a configuration-dependent authentication bypass in deployments where OAuth2 Proxy is used with an auth_request-style integration (such as nginx auth_request) and either --ping-user-agent is set or --gcp-healthchecks is enabled. In affected configurations, OAuth2 Proxy treats any request with the configured health check User-Agent value as a successful health check regardless of the requested path, allowing an unauthenticated remote attacker to bypass authentication and access protected upstream resources. Deployments that do not use auth_request-style subrequests or that do not enable --ping-user-agent/--gcp-healthchecks are not affected. This issue is fixed in 7.15.2.

AnalysisAI

Authentication bypass in OAuth2 Proxy versions before 7.15.2 allows remote unauthenticated attackers to access protected resources when deployed with nginx auth_request integration and health check features enabled. Attackers can spoof health check User-Agent headers to bypass OAuth2 authentication entirely, gaining unauthorized access to upstream applications. CVSS 9.1 (Critical) reflects network-accessible, low-complexity attack requiring no privileges or user interaction. No active exploitation confirmed (not in CISA KEV), but the trivial attack complexity and authentication bypass impact warrant immediate patching in affected deployments using nginx auth_request with --ping-user-agent or --gcp-healthchecks flags.

Technical ContextAI

OAuth2 Proxy is a reverse proxy that enforces OAuth2 authentication before forwarding requests to upstream services. In nginx deployments, the auth_request directive creates subrequests to OAuth2 Proxy to validate authentication before serving protected content. The vulnerability (CWE-290: Authentication Bypass by Spoofing) stems from improper health check request validation. When --ping-user-agent or --gcp-healthchecks is configured, OAuth2 Proxy is intended to respond successfully to health monitoring probes matching specific User-Agent strings. However, affected versions fail to restrict this health check logic to designated health check endpoints, treating ANY request with the configured health check User-Agent as valid regardless of the requested path. This allows attackers to craft HTTP requests with spoofed User-Agent headers to bypass authentication checks entirely, as the proxy returns successful authentication responses to nginx for what should be protected resources. The flaw only manifests in auth_request-style integrations where the proxy's response directly determines access control decisions.

RemediationAI

Immediately upgrade OAuth2 Proxy to version 7.15.2 or later, which contains fixes for the authentication bypass vulnerability. The patched release is available at https://github.com/oauth2-proxy/oauth2-proxy/releases/tag/v7.15.2 with complete remediation for the health check validation flaw. Organizations unable to upgrade immediately should disable --ping-user-agent and --gcp-healthchecks configuration flags as a temporary mitigation, though this impacts health monitoring capabilities. Alternative interim mitigation involves restricting health check endpoints at the nginx level to specific paths and removing auth_request directives from those locations, ensuring health checks do not bypass authentication validation for protected resources. Review nginx configuration to ensure auth_request integration properly isolates health check endpoints from application paths. Consult the GitHub security advisory at https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-5hvv-m4w4-gf6v for deployment-specific guidance and configuration validation steps.