CVE-2011-1757 in DJabberd
Summary
by MITRE
DJabberd 0.84 and earlier does not properly detect recursion during entity expansion, which allows remote attackers to cause a denial of service (memory and CPU consumption) via a crafted XML document containing a large number of nested entity references, a similar issue to CVE-2003-1564.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 11/13/2021
The vulnerability identified as CVE-2011-1757 affects DJabberd versions 0.84 and earlier, representing a critical weakness in XML processing capabilities that enables remote attackers to execute denial of service attacks through carefully crafted malicious documents. This flaw specifically resides in the entity expansion mechanism within the XML parser implementation, where the system fails to adequately monitor or limit recursive entity references during document parsing operations. The vulnerability operates under the principle of XML external entity (XXE) processing, where maliciously constructed XML documents can trigger excessive resource consumption through nested entity references that expand infinitely without proper boundary checks.
The technical implementation of this vulnerability stems from insufficient input validation and boundary control mechanisms within the XML parser's entity resolution process. When a malformed XML document containing deeply nested entity references is processed, the parser attempts to resolve each entity reference recursively, leading to exponential memory consumption and CPU utilization spikes. This behavior creates a resource exhaustion condition that can render the affected system unusable, effectively preventing legitimate users from accessing services while consuming all available computational resources. The vulnerability directly maps to CWE-400, which classifies the weakness as "Uncontrolled Resource Consumption" and aligns with ATT&CK technique T1499.100, specifically targeting "Application Exhaustion Flood" as part of the resource exhaustion attack patterns.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by attackers to perform sustained denial of service attacks that may go unnoticed until significant system resources are consumed. The memory and CPU consumption patterns created by recursive entity expansion can cause cascading failures throughout the system, potentially affecting other services running on the same infrastructure. Attackers can craft XML documents with minimal payload that, when processed, generate massive resource consumption, making the attack both efficient and difficult to detect through conventional monitoring systems. The vulnerability's similarity to CVE-2003-1564 demonstrates a persistent pattern in XML processing implementations where recursive entity handling lacks proper safeguards, indicating that this represents a fundamental architectural weakness rather than an isolated incident.
Mitigation strategies for CVE-2011-1757 require immediate implementation of XML parser configuration changes that enforce strict limits on entity expansion, including disabling external entity resolution entirely and implementing maximum entity expansion depth controls. System administrators should upgrade to DJabberd versions that have addressed this vulnerability through proper input validation and resource consumption monitoring. Network-level protections such as XML filtering appliances and intrusion prevention systems can help detect and block malicious XML traffic before it reaches the vulnerable application. Additionally, implementing proper resource limits and monitoring for abnormal CPU and memory usage patterns can help identify exploitation attempts and prevent complete system compromise. Organizations should also consider implementing application firewalls and input validation layers that can identify and block malformed XML content before it reaches the core parsing engine, as this represents a fundamental security gap in the XML processing architecture that requires both immediate remediation and long-term architectural improvements to prevent similar issues from emerging in future implementations.