CVE-2025-31492 in mod_auth_openidc
Summary
by MITRE • 04/06/2025
mod_auth_openidc is an OpenID Certified authentication and authorization module for the Apache 2.x HTTP server that implements the OpenID Connect Relying Party functionality. Prior to 2.4.16.11, a bug in a mod_auth_openidc results in disclosure of protected content to unauthenticated users. The conditions for disclosure are an OIDCProviderAuthRequestMethod POST, a valid account, and there mustn't be any application-level gateway (or load balancer etc) protecting the server. When you request a protected resource, the response includes the HTTP status, the HTTP headers, the intended response (the self-submitting form), and the protected resource (with no headers). This is an example of a request for a protected resource, including all the data returned. In the case where mod_auth_openidc returns a form, it has to return OK from check_userid so as not to go down the error path in httpd. This means httpd will try to issue the protected resource. oidc_content_handler is called early, which has the opportunity to prevent the normal output being issued by httpd. oidc_content_handler has a number of checks for when it intervenes, but it doesn't check for this case, so the handler returns DECLINED. Consequently, httpd appends the protected content to the response. The issue has been patched in mod_auth_openidc versions >= 2.4.16.11.
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Analysis
by VulDB Data Team • 12/30/2025
The vulnerability described in CVE-2025-31492 affects the mod_auth_openidc module, which serves as an OpenID Connect Relying Party implementation for Apache 2.x servers. This module facilitates authentication and authorization processes by integrating with OpenID Connect providers. The flaw exists in versions prior to 2.4.16.11 and represents a critical access control bypass that allows unauthenticated users to gain access to protected resources. The vulnerability specifically manifests when the module operates under certain configuration conditions including OIDCProviderAuthRequestMethod set to POST, the presence of a valid account, and absence of application-level gateways or load balancers protecting the server infrastructure. This configuration creates a scenario where authentication mechanisms fail to properly enforce access controls, leading to unauthorized content disclosure.
The technical implementation of this vulnerability stems from a flaw in the content handling logic within the mod_auth_openidc module. When a user requests a protected resource, the module's oidc_content_handler function is invoked early in the processing pipeline. This handler contains multiple checks designed to intercept and handle authentication scenarios appropriately, but it fails to account for a specific edge case involving POST-based authentication methods. The handler returns DECLINED in this particular scenario, which causes the Apache HTTP server to proceed with normal response processing. This behavior occurs because the check_userid function must return OK to avoid triggering error handling paths in httpd, but this creates a race condition where the protected content gets appended to the response without proper authentication verification. The module's response includes HTTP status codes, headers, the intended self-submitting form, and the protected resource content itself, effectively exposing sensitive information to any user who can make the specific request pattern.
The operational impact of this vulnerability extends beyond simple information disclosure, representing a fundamental breakdown in the authentication and authorization framework. Attackers exploiting this vulnerability can bypass authentication mechanisms entirely when the specific conditions are met, potentially gaining access to sensitive data, restricted resources, or privileged functionality within the web application. The vulnerability's exploitation requires specific environmental conditions including the POST authentication method and lack of intermediate protection layers, but once these conditions are satisfied, the exposure becomes complete. This makes the vulnerability particularly dangerous in environments where organizations rely on mod_auth_openidc for access control but may not have additional protective measures in place. The issue affects web applications that depend on OpenID Connect for authentication, potentially compromising user sessions, confidential data, or system resources that should remain protected.
Security mitigations for CVE-2025-31492 primarily involve upgrading to mod_auth_openidc version 2.4.16.11 or later, which contains the necessary code fixes to prevent the improper content handling. Organizations should also implement additional protective measures such as deploying load balancers or application firewalls that can intercept and filter unauthorized access attempts. The vulnerability aligns with CWE-284, which addresses improper access control in software systems, and demonstrates how authentication bypass flaws can create severe security implications in web server modules. From an ATT&CK framework perspective, this vulnerability maps to T1078, which covers valid accounts and T1566, which addresses credential harvesting, as it allows unauthorized access through legitimate authentication paths. System administrators should conduct immediate vulnerability assessments to identify affected installations and ensure proper patch management protocols are in place. Additionally, monitoring for unusual authentication patterns or unauthorized access attempts can help detect exploitation attempts before they result in successful breaches of protected content.