CVE-2016-2146 in mod_auth_mellon
Summary
by MITRE
The am_read_post_data function in mod_auth_mellon before 0.11.1 does not limit the amount of data read, which allows remote attackers to cause a denial of service (worker process crash, web server deadlock, or memory consumption) via a large amount of POST data.
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Analysis
by VulDB Data Team • 07/25/2022
The vulnerability identified as CVE-2016-2146 resides within the mod_auth_mellon module for the Apache HTTP Server, specifically affecting versions prior to 0.11.1. This authentication module implements SAML 2.0 authentication and is commonly used in enterprise environments for single sign-on solutions. The flaw manifests in the am_read_post_data function which processes incoming POST requests during the authentication flow. When this function fails to enforce any limits on the amount of data it reads from POST requests, it creates a critical security gap that can be exploited by malicious actors.
The technical implementation of this vulnerability stems from inadequate input validation and resource management within the authentication module. The am_read_post_data function processes SAML authentication requests that typically contain large XML documents, but without any mechanism to cap the maximum data size that can be read. This allows an attacker to submit arbitrarily large POST requests to the web server, causing the worker processes to consume excessive memory resources or become unresponsive. The vulnerability operates at the application layer and can be exploited through standard HTTP POST requests without requiring any authentication credentials or privileged access.
The operational impact of CVE-2016-2146 is severe and multifaceted, potentially leading to complete service disruption for affected web applications. Remote attackers can trigger denial of service conditions by causing worker process crashes, leading to web server deadlock scenarios where the server becomes unresponsive to legitimate requests. Additionally, the excessive memory consumption can gradually exhaust system resources, making the server unable to handle additional legitimate requests. This vulnerability affects the availability aspect of the CIA triad and can be particularly devastating in production environments where authentication services are critical for business operations. The attack can be executed from any network location with access to the vulnerable web server, making it a significant concern for publicly exposed authentication endpoints.
Organizations affected by this vulnerability should immediately upgrade to mod_auth_mellon version 0.11.1 or later, which implements proper data size limitations to prevent resource exhaustion attacks. System administrators should also implement additional monitoring and rate-limiting mechanisms to detect and prevent abnormal POST request patterns. Network-level mitigations such as implementing web application firewalls with content inspection capabilities can help detect and block malicious POST requests before they reach the vulnerable module. The vulnerability aligns with CWE-770, which addresses allocation of resources without reasonable limits, and can be categorized under ATT&CK technique T1499.004 for resource exhaustion attacks. Organizations should also conduct regular security assessments of their authentication modules and maintain up-to-date vulnerability management processes to prevent similar issues from occurring in other components of their web infrastructure.