CVE-2006-6919 in Sage
Summary
by MITRE
Firefox Sage extension 1.3.8 and earlier allows remote attackers to execute arbitrary Javascript in the local context via an RSS feed with an img tag containing the script followed by an extra trailing ">", which Sage modifies to close the img element before the malicious script.
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Analysis
by VulDB Data Team • 05/24/2025
The vulnerability identified as CVE-2006-6919 affects the Firefox Sage extension version 1.3.8 and earlier, representing a critical cross-site scripting flaw that enables remote code execution within the local context of affected browsers. This issue stems from improper handling of RSS feed content by the Sage extension, which processes and renders RSS feeds within the Firefox environment. The vulnerability specifically targets the extension's HTML parsing mechanism when encountering img tags that contain embedded JavaScript code, creating a dangerous condition where malicious actors can inject arbitrary JavaScript into the browser's local execution context.
The technical flaw manifests through a sophisticated payload construction technique where attackers craft RSS feed entries containing img tags with embedded script code followed by an extra trailing ">" character. This seemingly innocuous character triggers a specific parsing behavior within the Sage extension's HTML processing engine, causing the extension to modify the malformed img tag in a way that inadvertently closes the img element before executing the malicious script. The extension's HTML sanitization process fails to properly handle this edge case, leading to the execution of JavaScript code in the local context of the browser, bypassing normal security boundaries that typically protect against such attacks.
The operational impact of this vulnerability extends far beyond simple script execution, as it allows attackers to perform actions that would normally be restricted to the local file system or browser environment. An attacker could potentially access local files, manipulate browser settings, steal session cookies, or perform other malicious activities that compromise the user's browsing environment and data security. This vulnerability particularly affects users who rely on the Sage extension for RSS feed aggregation, making it a significant risk for anyone who consumes RSS feeds through this specific browser extension, as the attack can be executed without any user interaction beyond viewing the malicious feed.
The vulnerability aligns with CWE-79, which describes cross-site scripting flaws in web applications and extensions, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for scripting languages, specifically targeting browser-based scripting environments. Organizations and users should immediately update to Sage extension versions that address this vulnerability, as the flaw represents a serious security risk that can be exploited remotely without user awareness. The recommended mitigation strategy involves not only updating the extension to a patched version but also implementing additional security measures such as network-based filtering of RSS feed content and user education regarding the risks of consuming untrusted RSS feeds. Security administrators should also monitor for similar parsing vulnerabilities in other browser extensions and implement comprehensive patch management processes to ensure all browser add-ons remain current with security updates.