CVE-2016-3163 in Drupal
Summary
by MITRE
The XML-RPC system in Drupal 6.x before 6.38 and 7.x before 7.43 might make it easier for remote attackers to conduct brute-force attacks via a large number of calls made at once to the same method.
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Analysis
by VulDB Data Team • 10/05/2018
The vulnerability identified as CVE-2016-3163 affects Drupal content management systems version 6.x prior to 6.38 and 7.x prior to 7.43, specifically within the XML-RPC system implementation. This weakness creates a significant security risk by enabling remote attackers to conduct brute-force authentication attacks with enhanced efficiency. The vulnerability stems from insufficient rate limiting and concurrency controls within the XML-RPC interface, which allows malicious actors to flood the system with simultaneous requests targeting the same authentication method. The XML-RPC protocol in these vulnerable versions lacks proper mechanisms to detect and throttle excessive request volumes, making it particularly susceptible to automated attack vectors that exploit the system's inability to distinguish legitimate traffic from malicious brute-force attempts.
The technical flaw manifests in the absence of effective rate limiting mechanisms within the XML-RPC subsystem, which operates under the Common Weakness Enumeration classification of CWE-307 - Improper Restriction of Excessive Authentication Attempts. This weakness directly enables credential stuffing and brute-force attacks by allowing attackers to rapidly submit multiple authentication requests to the same endpoint without sufficient system controls to prevent such behavior. The vulnerability specifically impacts the authentication mechanisms that utilize XML-RPC interfaces, where the system fails to implement adequate concurrency controls or request throttling measures. Attackers can leverage this flaw to systematically test numerous credential combinations against the vulnerable Drupal installations, significantly increasing their chances of successful unauthorized access.
The operational impact of this vulnerability extends beyond simple authentication bypass attempts, as it provides attackers with a scalable method for conducting automated attacks against Drupal systems. The vulnerability aligns with techniques documented in the MITRE ATT&CK framework under the T1110 - Brute Force category, where adversaries exploit weak authentication controls to gain unauthorized access. Organizations running affected Drupal versions face increased risk of account takeovers, data breaches, and potential system compromise when this vulnerability remains unpatched. The distributed nature of the attack, combined with the ability to make numerous concurrent calls, makes detection and mitigation more challenging for security operations teams. Additionally, the vulnerability affects systems that rely on XML-RPC for legitimate administrative functions, potentially disrupting normal operations while attackers attempt to exploit the weakness.
Effective mitigations for CVE-2016-3163 include immediate patching of affected Drupal installations to versions 6.38 and 7.43 or later, which contain proper rate limiting and concurrency controls. Organizations should also implement network-level rate limiting measures and intrusion detection systems to monitor for unusual patterns of XML-RPC traffic. The implementation of account lockout mechanisms and multi-factor authentication can provide additional defense-in-depth layers against brute-force attacks. Security teams should review and configure appropriate logging controls to monitor authentication attempts and detect potential abuse of the XML-RPC interface. The vulnerability demonstrates the importance of implementing proper access controls and rate limiting as fundamental security measures within web applications, particularly those that expose remote procedure call interfaces. Organizations should also consider disabling XML-RPC functionality entirely if it is not required for business operations, as this eliminates the attack surface associated with this particular vulnerability.