CVE-2021-45085 in Epiphany
Summary
by MITRE • 12/16/2021
XSS can occur in GNOME Web (aka Epiphany) before 40.4 and 41.x before 41.1 via an about: page, as demonstrated by ephy-about:overview when a user visits an XSS payload page often enough to place that page on the Most Visited list.
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Analysis
by VulDB Data Team • 12/22/2021
The vulnerability CVE-2021-45085 represents a cross-site scripting flaw in GNOME Web browser known as Epiphany that affects versions prior to 40.4 and 41.x before 41.1. This vulnerability specifically exploits the browser's handling of about: pages, which are special browser pages used for displaying internal information and user interface elements. The attack vector is particularly concerning because it leverages the browser's Most Visited list functionality, which automatically populates with frequently visited pages to enhance user experience.
The technical implementation of this vulnerability stems from insufficient input validation and output sanitization within the about: page processing mechanism. When a user visits a malicious page containing XSS payload code and navigates to it frequently enough to be added to the Most Visited list, the browser fails to properly sanitize the page content before rendering it in the about:overview context. This creates a persistent XSS condition where malicious scripts can execute within the browser's privileged context, potentially compromising user sessions and data.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with the ability to establish persistent footholds within the browser environment. Since the Most Visited list is a frequently accessed feature, the malicious payload can remain active for extended periods without requiring repeated user interaction. This aligns with CWE-79 Cross-site Scripting attack patterns where the vulnerability exists in the data handling process rather than the core browser functionality itself. The attack requires minimal user interaction beyond normal browsing behavior, making it particularly dangerous in real-world scenarios.
Security implications of this vulnerability include potential session hijacking, credential theft, and data exfiltration from the compromised browser environment. The ATT&CK framework categorizes this as a technique involving client-side exploitation where the adversary leverages browser vulnerabilities to execute malicious code. The vulnerability's persistence through the Most Visited list functionality makes it particularly effective for maintaining access over time, as users regularly interact with this feature. Organizations using GNOME Web browser should immediately update to versions 40.4 or 41.1 and higher to mitigate this risk, as the flaw represents a significant security gap in the browser's input sanitization processes.
The vulnerability demonstrates the importance of comprehensive security testing for browser components, particularly those handling privileged internal pages. It highlights how seemingly benign features like Most Visited lists can become attack vectors when proper input validation is absent. This particular flaw underscores the need for consistent security practices across all browser components, including internal pages that may not receive the same level of scrutiny as external web content processing.