CVE-2011-3288 in Unified Presence
Summary
by MITRE
Cisco Unified Presence before 8.5(4) does not properly detect recursion during entity expansion, which allows remote attackers to cause a denial of service (memory and CPU consumption, and process crash) via a crafted XML document containing a large number of nested entity references, aka Bug IDs CSCtq89842 and CSCtq88547, a similar issue to CVE-2003-1564.
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Analysis
by VulDB Data Team • 11/23/2021
The vulnerability described in CVE-2011-3288 represents a classic example of a denial of service attack leveraging XML entity expansion recursion within Cisco Unified Presence systems. This flaw exists in versions prior to 8.5(4) and demonstrates how seemingly benign XML processing can become a significant security concern when proper safeguards are absent. The vulnerability specifically affects the entity expansion mechanism that processes XML documents, creating a scenario where recursive entity references can consume system resources without proper bounds checking. The issue is particularly concerning because it allows remote attackers to exploit this weakness from outside the network perimeter, making it accessible to a wide range of potential threat actors.
The technical implementation of this vulnerability stems from inadequate validation of XML entity references during the parsing process. When the Cisco Unified Presence system encounters a crafted XML document containing deeply nested entity references, it fails to properly detect and terminate the recursive expansion process. This allows the system to continuously expand entities, leading to exponential memory consumption and CPU utilization. The vulnerability operates at the application layer and specifically targets the XML parser component responsible for processing incoming presence data. According to CWE-400, this maps to a weakness involving resource exhaustion due to inadequate input validation and bounds checking. The recursive nature of the attack means that even a relatively small crafted XML document can trigger significant system degradation, as each entity expansion multiplies the processing requirements exponentially.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability and reliability of unified communication services within enterprise environments. When exploited successfully, the vulnerability can cause processes to crash and consume excessive system resources, leading to complete service outages for users relying on Cisco Unified Presence for instant messaging, presence information, and collaboration services. The memory and CPU consumption patterns suggest that the system may become unresponsive to legitimate traffic while processing the malicious XML content, effectively creating a denial of service condition. This type of attack aligns with ATT&CK technique T1499.004, which covers network disruption by exhausting resources, and represents a significant risk to business continuity in organizations that depend on unified communication platforms. The vulnerability's similarity to CVE-2003-1564 indicates a persistent pattern in XML processing flaws that have been observed across multiple vendors and time periods, emphasizing the importance of robust input validation.
Mitigation strategies for this vulnerability primarily focus on implementing proper XML parsing controls and upgrading to patched versions of Cisco Unified Presence. Organizations should ensure they are running Cisco Unified Presence version 8.5(4) or later, which includes fixes for this specific recursion detection issue. Network segmentation and access controls can help limit exposure by restricting access to the affected system to trusted sources only. Implementing XML validation rules and setting reasonable limits on entity expansion depths can provide additional protection layers. Security monitoring should include detection of unusual memory and CPU usage patterns that might indicate exploitation attempts. The fix typically involves implementing proper recursion detection mechanisms within the XML parser, ensuring that entity expansion processes are bounded and terminated when appropriate limits are reached. Organizations should also consider implementing rate limiting and input validation for all XML processing components to prevent similar vulnerabilities from occurring in other systems. Regular security assessments and vulnerability scanning should be performed to identify and remediate similar issues in other network components that may be susceptible to XML-based attacks.