CVE-2009-2473 in neon
Summary
by MITRE
neon before 0.28.6, when expat is used, does not properly detect recursion during entity expansion, which allows context-dependent 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.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability identified as CVE-2009-2473 affects the neon library version 0.28.5 and earlier, specifically when the expat XML parser is utilized for processing XML documents. This flaw represents a classic example of a denial of service attack through resource exhaustion, where malicious actors can exploit the library's inadequate recursion detection mechanisms during entity expansion processes. The issue manifests when processing specially crafted XML documents that contain deeply nested entity references, creating a scenario where the parser fails to properly monitor and limit recursive expansion attempts.
The technical flaw resides in the library's XML parsing implementation where the entity expansion mechanism lacks proper safeguards against excessive recursion. When neon encounters XML documents containing numerous nested entity references, it continues to expand these entities without adequate depth monitoring or recursion limits, leading to exponential memory consumption and CPU utilization. This behavior creates a condition where the parser becomes overwhelmed by the recursive expansion process, consuming system resources at an unsustainable rate. The vulnerability is particularly concerning because it operates within the context of legitimate XML processing operations, making it difficult to distinguish between normal and malicious input at the network level.
The operational impact of this vulnerability extends beyond simple service disruption to encompass potential system instability and resource exhaustion across multiple application layers. Attackers can craft XML documents that trigger the recursive expansion behavior, causing memory allocation to spiral out of control while simultaneously consuming CPU cycles at an increasing rate. This resource consumption pattern can lead to complete system hangs, application crashes, or denial of service conditions that affect the availability of services relying on the affected library. The vulnerability's similarity to CVE-2003-1564 indicates a persistent pattern in XML parsing libraries where recursion detection mechanisms are insufficiently implemented, suggesting that this represents a systemic issue rather than an isolated incident.
Organizations utilizing the affected neon library versions should prioritize immediate remediation through patch updates to version 0.28.6 or later, which contain proper recursion detection and limit mechanisms. The implementation of input validation and XML document size restrictions can serve as additional defensive measures to prevent exploitation. Security teams should also implement monitoring for unusual memory and CPU consumption patterns when processing XML data, as these metrics can indicate potential exploitation attempts. From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1499.004 for resource exhaustion attacks and CWE-400 for unchecked resource allocation, highlighting the importance of proper input validation and resource management in XML processing libraries. The vulnerability demonstrates how seemingly routine operations in XML parsing can become attack vectors when proper safeguards are absent, emphasizing the critical need for robust recursion detection in parsing libraries used for processing untrusted data.