CVE-2011-1157 in Universal Feed Parser
Summary
by MITRE
Cross-site scripting (XSS) vulnerability in feedparser.py in Universal Feed Parser (aka feedparser or python-feedparser) 5.x before 5.0.1 allows remote attackers to inject arbitrary web script or HTML via malformed XML comments.
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Analysis
by VulDB Data Team • 02/02/2025
The CVE-2011-1157 vulnerability represents a critical cross-site scripting flaw within the Universal Feed Parser library, specifically affecting versions 5.x prior to 5.0.1. This vulnerability resides in the feedparser.py module and demonstrates how XML parsing libraries can become attack vectors when inadequate input validation mechanisms are implemented. The flaw specifically targets the handling of malformed XML comments, which creates an avenue for malicious actors to inject arbitrary web scripts or HTML content into applications that rely on this feed parsing functionality.
The technical implementation of this vulnerability stems from insufficient sanitization of XML comment elements during the parsing process. When Universal Feed Parser encounters malformed XML comments, the parsing logic fails to properly escape or filter these elements before they are processed by downstream applications. This creates a scenario where an attacker can craft specially formatted XML feeds containing malicious scripts within comment sections that get executed when the parsed content is rendered in web browsers. The vulnerability operates under CWE-79 which specifically addresses cross-site scripting flaws, and aligns with ATT&CK technique T1212 which targets application security weaknesses through malformed input processing.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform session hijacking, steal sensitive user data, redirect users to malicious sites, or execute arbitrary commands within the context of the victim's browser. Applications that utilize Universal Feed Parser for aggregating content from external sources become vulnerable when they fail to implement proper input validation or output encoding for feed data. The attack surface is particularly broad since many web applications rely on RSS and Atom feed aggregation for content management, news feeds, or social media integration, making this vulnerability potentially exploitable across numerous platforms and services.
Organizations should implement immediate mitigations including upgrading to Universal Feed Parser version 5.0.1 or later, which contains the necessary patches to properly sanitize XML comment elements. Additional defensive measures include implementing strict input validation for all feed data, employing content security policies to prevent script execution, and using proper output encoding when displaying feed content in web interfaces. The vulnerability serves as a reminder of the critical importance of input validation in XML processing libraries and demonstrates how seemingly benign parsing operations can become security gateways when proper sanitization controls are absent. Security teams should also consider implementing automated monitoring for feed parsing activities and establish incident response procedures for handling potential XSS attacks originating from feed content sources.