CVE-2015-2316 in Django
Summary
by MITRE
The utils.html.strip_tags function in Django 1.6.x before 1.6.11, 1.7.x before 1.7.7, and 1.8.x before 1.8c1, when using certain versions of Python, allows remote attackers to cause a denial of service (infinite loop) by increasing the length of the input string.
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Analysis
by VulDB Data Team • 05/01/2022
The vulnerability identified as CVE-2015-2316 represents a critical denial of service weakness within the Django web framework's HTML sanitization utilities. This flaw specifically targets the utils.html.strip_tags function which is designed to remove HTML tags from strings while preserving the underlying content. The vulnerability manifests when processing certain input strings through the strip_tags function, creating conditions that can lead to infinite loops and subsequent system resource exhaustion. The issue affects multiple Django versions including 1.6.x before 1.6.11, 1.7.x before 1.7.7, and 1.8.x before 1.8c1, indicating a widespread impact across the framework's release cycles. The vulnerability's exploitation requires specific Python version combinations to trigger the problematic behavior, making it particularly insidious as it may not be immediately apparent during routine testing or development phases.
The technical root cause of this vulnerability stems from inadequate input validation and loop termination logic within the strip_tags implementation. When certain malformed HTML structures are processed through the function, the internal parsing algorithms can enter infinite loops due to improper state management during tag detection and removal. This occurs because the function fails to properly handle nested or malformed HTML constructs that cause the parsing loop to continuously iterate without making progress toward tag removal. The vulnerability is classified under CWE-835, which specifically addresses infinite loops in software implementations, making it a direct descendant of well-known software design flaws that have been documented in security literature for decades. The infinite loop condition consumes excessive CPU cycles and can lead to complete system unresponsiveness, particularly when exploited through web requests that trigger the vulnerable code path.
The operational impact of CVE-2015-2316 extends beyond simple service disruption to potentially enable more sophisticated attacks within the broader context of the MITRE ATT&CK framework's resource exhaustion tactics. An attacker can leverage this vulnerability to perform denial of service attacks against Django applications by submitting carefully crafted HTML content that triggers the infinite loop condition. The attack vector typically involves sending maliciously formatted HTML strings through web forms, API endpoints, or other input mechanisms that eventually pass through the strip_tags function. When exploited successfully, the vulnerability can cause application servers to become unresponsive, leading to service degradation or complete application failure. This makes it particularly dangerous in production environments where application availability is critical for business operations, potentially affecting thousands of concurrent users depending on the application's scale and resource allocation.
Mitigation strategies for CVE-2015-2316 primarily focus on immediate patching and application hardening measures. Organizations should prioritize upgrading to patched versions of Django including 1.6.11, 1.7.7, or 1.8c1 to eliminate the vulnerability entirely. In cases where immediate patching is not feasible, implementing input validation and length restrictions can provide temporary protection by limiting the size and complexity of HTML content processed through the vulnerable function. Application-level defenses should include rate limiting mechanisms to prevent abuse of the vulnerable code path and monitoring systems to detect unusual CPU consumption patterns that may indicate exploitation attempts. Additionally, implementing proper error handling and timeout mechanisms within the application code can help prevent exploitation from causing complete system failures. Security teams should also consider implementing web application firewalls that can detect and block malicious input patterns associated with this vulnerability, aligning with ATT&CK techniques that focus on preventing command execution and resource exhaustion attacks. The vulnerability serves as a reminder of the importance of thorough input validation and the potential consequences of inadequate state management in security-critical code components.