CVE-2012-2921 in Universal Feed Parser
Summary
by MITRE
Universal Feed Parser (aka feedparser or python-feedparser) before 5.1.2 allows remote attackers to cause a denial of service (memory consumption) via a crafted XML ENTITY declaration in a non-ASCII encoded document.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability identified as CVE-2012-2921 affects the Universal Feed Parser library, commonly known as feedparser or python-feedparser, which is widely used for parsing RSS and Atom feeds in Python applications. This flaw exists in versions prior to 5.1.2 and represents a significant security concern that can be exploited by remote attackers to consume excessive system memory. The vulnerability specifically targets the library's handling of XML ENTITY declarations within non-ASCII encoded documents, creating a condition where maliciously crafted feed content can trigger unbounded memory allocation. The issue stems from the library's insufficient validation and processing of entity references, particularly when these entities are defined in encodings other than ASCII. This type of vulnerability falls under the category of memory exhaustion attacks and aligns with CWE-400, which addresses unchecked resource consumption, and more specifically CWE-770, which deals with allocation of resources without limits or with inadequate limits. The attack vector requires an attacker to craft a malicious XML document containing carefully constructed ENTITY declarations that, when processed by the vulnerable feedparser library, cause the parser to allocate excessive memory resources. The operational impact of this vulnerability extends beyond simple denial of service, as it can potentially crash applications that rely on feedparser, leading to service disruption and affecting the availability of systems that consume feeds from untrusted sources. This weakness is particularly dangerous in web applications, content management systems, and any software that automatically fetches and processes feeds from external sources without proper sanitization. The vulnerability is consistent with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through resource exhaustion attacks. When exploited, the malicious entity declarations can cause the parser to recursively expand entities or allocate memory in a manner that grows without bounds, effectively consuming all available system memory and potentially causing system instability or complete system crashes. The risk is amplified in environments where feedparser is used to process feeds from untrusted third parties, as attackers can craft malicious feeds that appear legitimate but contain the exploitable entity declarations. Organizations using this library are particularly vulnerable if they do not implement proper input validation, feed sanitization, or rate limiting mechanisms when processing external feeds. The fix for this vulnerability required modifications to the feedparser library's entity handling logic to implement proper bounds checking and limit the expansion of entity references. This demonstrates the importance of proper resource management in XML parsers and highlights how seemingly innocuous XML features can become security risks when not properly constrained. The vulnerability serves as a reminder of the critical need for input validation in parsing libraries and the potential for XML-related attacks to impact system availability. Security practitioners should ensure that all applications using feedparser or similar feed processing libraries are updated to version 5.1.2 or later, as this update addresses the memory consumption issue through enhanced entity handling and proper resource allocation limits. Additionally, implementing proper feed sanitization and validation processes can provide additional defense in depth against similar vulnerabilities in other components of the application stack. The vulnerability also underscores the necessity of regularly updating third-party libraries and maintaining awareness of security advisories for commonly used components in application development. Organizations should consider implementing automated dependency scanning to identify vulnerable components and ensure timely patching across their software ecosystems.