CVE-2011-1783 in Subversion
Summary
by MITRE
The mod_dav_svn module for the Apache HTTP Server, as distributed in Apache Subversion 1.5.x and 1.6.x before 1.6.17, when the SVNPathAuthz short_circuit option is enabled, allows remote attackers to cause a denial of service (infinite loop and memory consumption) in opportunistic circumstances by requesting data.
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Analysis
by VulDB Data Team • 12/08/2024
The vulnerability identified as CVE-2011-1783 affects the mod_dav_svn module within the Apache HTTP Server ecosystem, specifically impacting Apache Subversion versions 1.5.x and 1.6.x prior to 1.6.17. This security flaw manifests when the SVNPathAuthz short_circuit option is enabled, creating a condition where remote attackers can exploit the module to induce a denial of service scenario. The vulnerability operates through opportunistic circumstances where specific request patterns can trigger the problematic behavior, making it particularly concerning for systems that rely on Subversion's web-based access controls.
The technical mechanism behind this vulnerability stems from improper handling of authorization checks within the mod_dav_svn module when the short_circuit option is active. When this configuration is enabled, the module attempts to optimize authorization processing by short-circuiting certain checks, but this optimization contains a flaw that can lead to infinite loops during specific request processing sequences. The flaw manifests as the module entering a recursive or iterative loop when processing certain data requests, causing continuous memory allocation without proper termination conditions. This behavior results in excessive resource consumption that can eventually exhaust system memory and render the service unavailable to legitimate users.
The operational impact of CVE-2011-1783 extends beyond simple service disruption, as it represents a significant threat to system availability and stability within organizations relying on Apache Subversion for version control management. Attackers can exploit this vulnerability to consume system resources indefinitely, potentially leading to complete service unavailability and system instability. The opportunistic nature of the attack means that the vulnerability may not be immediately exploitable but can be triggered under specific conditions that arise during normal usage patterns, making it particularly dangerous for production environments where continuous availability is critical. This type of denial of service vulnerability directly violates the availability principles outlined in the CIA triad and can have cascading effects on development workflows and collaborative software projects.
Systems affected by this vulnerability should implement immediate mitigations including upgrading to Apache Subversion version 1.6.17 or later, which contains the necessary patches to address the infinite loop condition. Organizations should also consider disabling the SVNPathAuthz short_circuit option if it is not essential for their operational requirements, as this configuration change can prevent the vulnerable code path from being executed. Additionally, network-level protections such as rate limiting and connection throttling can help mitigate the impact of potential exploitation attempts, though these measures do not address the root cause. The vulnerability aligns with CWE-835, which describes the weakness of an infinite loop or infinite recursion, and represents a classic example of how optimization efforts can introduce security flaws that affect system availability. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to network denial of service and demonstrates the importance of proper input validation and resource management in web server modules. Organizations should also implement monitoring solutions to detect unusual memory consumption patterns that could indicate exploitation attempts, as the vulnerability's effects are measurable through system resource utilization metrics.