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OIDCProviderAuthRequestMethod POST leaks protected data

High
zandbelt published GHSA-59jp-rwph-878r Apr 6, 2025

Package

mod_auth_openidc

Affected versions

<= 2.4.16.10

Patched versions

>= 2.4.16.11

Description

Impact

A bug in a mod_auth_openidc results in disclosure of protected content to unauthenticated users.
The conditions for disclosure are:

  • OIDCProviderAuthRequestMethod POST.
  • Require valid-user
  • 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. (The content-length in the response headers corresponds to the start of the second tag.)

----- Request ----

GET /foo/ HTTP/1.1
Accept: */*
Host: xxxxxxxxxxxxxxxxxxxxxxxx

----- Response ----

HTTP/1.1 200 OK
Date: Wed, 02 Apr 2025 14:54:43 GMT
Server: Apache/2.4.63 (Unix) OpenSSL/3.0.2
Set-Cookie: mod_auth_openidc_state_Zjv-eHqSy08Do6CPJXYD-j_BJFk=eyJhbGciOiAiZGlyIiwgImVuYyI6ICJBMjU2R0NNIn0..DBQVvz1XSoTv7Pw0.d-DFmTTyBeu9nfGm0xaiJLBhsLSZLU4_PgpMwZi0-YmzzARn8sxjxuQc1yPiWMJ8Y0nCkyRP-VIn6VeOFNoHeKzIror1AMW5h1Wop0yky72x-o49Pc4SVKsF1T6p2jw8mZHow9VEC-HIaQilyzEBz5xoXp890KS5ih88NDj2nTulNOmQ56g_51osYx5N0sx-_i-EUsLNlxNgKXax37OckWtCzXCHT-TqYS5PJDoAQ6RAPGvgVnF48Nz9a0EN5aDhZfHQjIH46tjhca748A-Ft1LyMx3m3hkk3fU.fWYAzT6ukboFUu1EBUlKCg; Path=/; Secure; HttpOnly; SameSite=Lax
Content-Length: 1139
Content-Type: text/html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>Submitting...</title>
    
  </head>
  <body onload="document.forms[0].submit()">
    <p>Submitting Authentication Request...</p>
    <form method="post" action="https://login.windows.net/12345678-bdfa-4b79-ade3-1234567886e9/oauth2/authorize">
      <p>
      <input type="hidden" name="response_type" value="code">
      <input type="hidden" name="scope" value="openid">
      <input type="hidden" name="client_id" value="12345678-6ace-4f90-123456784cc1a1903">
      <input type="hidden" name="state" value="Zjv-eHqSy08Do6CPJXYD-j_BJFk">
      <input type="hidden" name="redirect_uri" value="https://xxxxxxxxxxxxxxxxxxxxxxxx/oidc/replyurl">
      <input type="hidden" name="nonce" value="JdBL0iVP-lu_F4rC4PvqVBCVRs0yrt3QVhWeZE5mRc4">
      <input type="hidden" name="code_challenge" value="Aj3j4CyhXwBIhGNkAO-fVB0v149dE7YxXNsQ03ROyGc">
      <input type="hidden" name="code_challenge_method" value="S256">
      </p>
    </form>

  </body>
</html>

<html><body><h1>Protected page</h1><p>You shouldn't be able to see this.</p></body></html>
---- End of data ----

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.

It is hard to notice the error if you're using an http library to do requests - the invalid data will be silently dropped, a new connection will be created, and the end-user remains none the wiser. Constructing a client that shows the raw data on the wire reveals a very different story.

Patches

The issue has been patched in mod_auth_openidc versions >= 2.4.16.11.

Workarounds

If there is an application-level gateway protecting the server, it mitigates the problem by hiding the extra content from the outside world.
Switching to OIDCProviderAuthRequestMethod GET (which is the default) avoids the issue.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

CVE ID

CVE-2025-31492

Weaknesses

No CWEs

Credits