CVE-2026-76835 oauth2-proxy CVE debrief

Who should care

Administrators and security teams using OAuth2 Proxy in their infrastructure should assess their configurations and update them to restrict trusted proxies, ensuring that only legitimate sources can set the X-Forwarded-Uri header.

Why it matters

This vulnerability allows unauthenticated attackers to bypass authentication in OAuth2 Proxy, potentially leading to unauthorized access to protected resources. Administrators must review and update their configurations to restrict trusted proxies and prevent exploitation.

• Potential unauthorized access to protected resources
• Need for urgent configuration review and update
• Possible exposure of sensitive data

Technical summary

The vulnerability exists due to OAuth2 Proxy's improper handling of the X-Forwarded-Uri header. By default, the proxy trusts all proxies, allowing an attacker to spoof the URI and bypass authentication for protected upstream paths. This can lead to unauthorized access to sensitive resources. The issue is exacerbated by the default configuration of OAuth2 Proxy, which trusts all proxies. To mitigate this vulnerability, administrators must review and update their configurations to restrict trusted proxies and prevent exploitation.

Defensive priority

High

Recommended defensive actions

• Review and update OAuth2 Proxy configurations to restrict trusted proxies
• Implement additional authentication checks for upstream paths
• Monitor for suspicious activity and adjust allow lists as needed
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The vulnerability arises from OAuth2 Proxy's default configuration, which trusts all proxies. An attacker can bypass authentication by setting the X-Forwarded-Uri header to a value matching an allow-listed route.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.