CVE-2016-9452 in Drupal
Summary
by MITRE
The transliterate mechanism in Drupal 8.x before 8.2.3 allows remote attackers to cause a denial of service via a crafted URL.
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Analysis
by VulDB Data Team • 06/10/2019
The vulnerability identified as CVE-2016-9452 affects Drupal 8.x versions prior to 8.2.3 and centers on a flaw within the transliterate mechanism that processes URL aliases and path handling. This issue enables remote attackers to execute a denial of service attack by submitting carefully crafted URLs that trigger excessive resource consumption during the transliteration process. The vulnerability specifically targets how Drupal handles character encoding transformations when processing URLs, creating a condition where malicious input can cause the system to consume disproportionate computational resources.
The technical flaw resides in the transliterate functionality that converts non-ASCII characters into their ASCII equivalents for URL generation and path handling. When a malformed URL containing specially crafted Unicode sequences is processed, the transliterate mechanism enters an inefficient processing loop or consumes excessive memory allocations. This occurs because the implementation does not properly validate or limit the complexity of input sequences that require transliteration, allowing attackers to craft inputs that cause the system to perform unnecessary or excessive character conversion operations. The vulnerability is particularly dangerous because it operates at the core URL processing layer, making it accessible through standard web requests without requiring authentication or privileged access.
The operational impact of this vulnerability extends beyond simple service disruption, as it can effectively render a Drupal 8 website unavailable to legitimate users. Attackers can repeatedly submit malicious URLs to exhaust server resources such as memory, CPU cycles, and processing time, leading to complete denial of service conditions. The vulnerability is particularly concerning for high-traffic websites or those with limited computational resources, as even a small number of concurrent attack requests can overwhelm the system. Additionally, the attack can be executed at scale using automated tools, making it difficult to distinguish from legitimate traffic and complicating mitigation efforts.
Organizations affected by this vulnerability should immediately upgrade to Drupal 8.2.3 or later versions where the transliterate mechanism has been properly patched to validate input sequences and limit resource consumption during processing. Security teams should implement rate limiting mechanisms at the web server level to restrict the number of requests per second from individual clients, and consider deploying URL filtering rules that can identify and block suspicious Unicode sequences. The vulnerability aligns with CWE-400, which addresses excessive resource consumption, and maps to ATT&CK technique T1499.004 for denial of service attacks. Network monitoring should be enhanced to detect unusual patterns in URL processing and resource utilization spikes that may indicate exploitation attempts.