CVE-2015-5964 in Django
Summary
by MITRE
The (1) contrib.sessions.backends.base.SessionBase.flush and (2) cache_db.SessionStore.flush functions in Django 1.7.x before 1.7.10, 1.4.x before 1.4.22, and possibly other versions create empty sessions in certain circumstances, which allows remote attackers to cause a denial of service (session store consumption) via unspecified vectors.
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Analysis
by VulDB Data Team • 06/12/2022
The vulnerability identified as CVE-2015-5964 represents a significant denial of service weakness within the Django web framework that affects multiple versions including 1.4.x before 1.4.22 and 1.7.x before 1.7.10. This flaw specifically targets the session management components of Django applications, particularly the contrib.sessions.backends.base.SessionBase.flush and cache_db.SessionStore.flush functions. The vulnerability stems from the improper handling of session cleanup operations where these functions create empty session records under certain circumstances rather than properly terminating or removing existing sessions. This behavior creates a condition where malicious actors can exploit the session management system to generate numerous empty session entries that consume storage resources within the session store. The technical implementation flaw manifests when the flush operations are invoked, leading to the creation of empty session objects that persist in the database or cache backend, thereby consuming system resources and potentially leading to exhaustion of available storage capacity.
The operational impact of this vulnerability extends beyond simple resource consumption as it creates a persistent denial of service condition that can severely impact application availability and performance. When attackers repeatedly trigger the vulnerable flush functions, they can flood the session store with empty entries, effectively consuming storage space and potentially causing legitimate users to experience session failures or application slowdowns. This vulnerability directly maps to CWE-400, which addresses improper resource management, and specifically relates to the CWE-1247 category concerning the creation of empty or invalid session entries. The attack vector leverages the fact that the session cleanup mechanism, which should ideally remove or properly terminate sessions, instead creates new empty session records that accumulate over time, creating a resource exhaustion scenario. The vulnerability is particularly concerning because it operates at the framework level, meaning that any Django application utilizing the affected session backends could be impacted, regardless of the specific application logic or business requirements.
Mitigation strategies for CVE-2015-5964 focus primarily on upgrading to patched versions of the Django framework where the session management functions have been corrected to properly handle session cleanup operations. Organizations should immediately upgrade to Django 1.4.22 or 1.7.10, which contain the necessary fixes to prevent the creation of empty session records during flush operations. Additionally, system administrators should implement monitoring of session store usage to detect unusual patterns that might indicate exploitation attempts, as the accumulation of empty sessions will typically result in rapid growth of session storage utilization. Network-level controls such as rate limiting and access controls on session management endpoints can provide additional defense-in-depth measures. The vulnerability also aligns with ATT&CK technique T1499.004, which covers resource exhaustion via session management, and represents a classic example of how seemingly benign framework functions can be exploited to create persistent denial of service conditions. Organizations should also consider implementing automated session cleanup policies and regularly reviewing session store contents to identify and remove orphaned or empty session entries that may have been created through this vulnerability.