Introduction
A single misconfigured regex in a widely deployed authentication proxy can mean the difference between secure access and open doors for attackers. OAuth2-Proxy, a popular open-source authentication gateway used in Kubernetes and cloud-native environments, recently faced such a scenario with CVE-2025-54576. This vulnerability directly impacts organizations that rely on OAuth2-Proxy for access control, especially when using the skip_auth_routes configuration to exempt certain endpoints from authentication.
OAuth2-Proxy is an open-source project with significant adoption in cloud and enterprise environments. It acts as a reverse proxy providing OAuth 2.0 and OpenID Connect authentication for web applications, with integrations for major identity providers and orchestration platforms. Its flexibility and community-driven development have made it a go-to solution for secure ingress in microservices architectures.
Technical Information
CVE-2025-54576 is rooted in how OAuth2-Proxy (versions 7.10.0 and below) processes the skip_auth_routes configuration option. This feature allows administrators to specify regex patterns for paths that should bypass authentication. The intended behavior is to match these patterns against the request path only.
However, the implementation flaw is that skip_auth_routes matches the regex against the entire request URI, including query parameters. This means that a pattern such as:
skip_auth_routes = [ "^/foo/.*/bar$" ]
which is intended to match only /foo/something/bar, will also match requests like /foo/critical_endpoint?param=/bar because the query parameter param=/bar satisfies the regex ending. This results in authentication being skipped for requests that should have been protected.
The root cause is in the request matching logic, specifically in the following files:
The vulnerable logic evaluates the regex against the full URI, not just the path, allowing attackers to craft URLs with query parameters that trigger unintended matches. Deployments using broad or wildcard regex patterns in skip_auth_routes are especially at risk.
Patch Information
In response to the identified vulnerability in OAuth2-Proxy's skip_auth_routes configuration, the development team has released version 7.11.0, which addresses the issue by modifying how the skip_auth_routes patterns are matched. Previously, these patterns were applied to the full request URI, including both the path and query parameters. This approach allowed attackers to craft URLs with query parameters that could bypass authentication mechanisms.
The patch changes the matching behavior to consider only the request path, excluding query parameters. This ensures that the skip_auth_routes patterns function as intended, preventing unauthorized access through manipulated query strings.
For example, if the configuration includes skip_auth_routes = [ "^/foo/.*/bar$" ], the intended behavior is to allow access to paths like /foo/something/bar. With the patch, this pattern will no longer match unintended URLs such as /foo/critical_endpoint?param=/bar, thereby enhancing security.
To implement this fix, users should upgrade to OAuth2-Proxy version 7.11.0 or later. Additionally, it's advisable to review existing skip_auth_routes configurations to ensure that regex patterns are appropriately defined and do not inadvertently allow access to sensitive endpoints.
Reference: GitHub Security Advisory GHSA-7rh7-c77v-6434
Detection Methods
Detecting exploitation of CVE-2025-54576 requires a multi-faceted approach, focusing on log analysis, network monitoring, and the deployment of specific detection rules. While direct access to detailed detection methods for this specific CVE is limited, we can draw parallels from similar vulnerabilities to outline effective detection strategies.
Log Analysis:
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Application Logs: Monitor application logs for unusual entries that may indicate exploitation attempts. For instance, look for error messages or stack traces that deviate from normal application behavior.
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System Logs: Examine system logs for signs of unauthorized access or privilege escalation.
Network Monitoring:
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Anomalous Traffic: Monitor network traffic for unusual patterns, such as unexpected outbound connections or data exfiltration attempts.
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Suspicious Domains: Keep an eye on connections to known malicious IPs or domains, which could indicate command and control (C2) communications.
Detection Rules:
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YARA Rules: Develop YARA rules to identify malicious payloads or scripts associated with the exploitation of similar vulnerabilities.
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Sigma Rules: Implement Sigma rules to detect specific patterns in logs that may indicate exploitation attempts.
Monitoring Guidance:
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Endpoint Detection and Response (EDR): Deploy EDR solutions to monitor for suspicious processes or behaviors on endpoints.
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Intrusion Detection Systems (IDS): Utilize IDS to detect and alert on network-based indicators of compromise.
By integrating these detection methods, organizations can enhance their ability to identify and respond to potential exploitation of CVE-2025-54576.
Affected Systems and Versions
- Product: OAuth2-Proxy
- Affected versions: 7.10.0 and below
- Vulnerable configuration: Deployments using
skip_auth_routeswith regex patterns, especially those containing wildcards or broad matching expressions
Vendor Security History
OAuth2-Proxy has previously addressed security issues such as:
- CVE-2021-21291: Open redirect in whitelist domain feature (prior to 7.0.0)
- CVE-2020-5233: Open redirect via crafted redirect URLs (prior to 5.0)
The project maintains a rapid patch response and has a mature process for handling security advisories via GitHub. Community engagement and regular updates contribute to its overall security posture.