CVE-2019-18209 in Etherpad-Lite
Summary
by MITRE
templates/pad.html in Etherpad-Lite 1.7.5 has XSS when the browser does not encode the path of the URL, as demonstrated by Internet Explorer.
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Analysis
by VulDB Data Team • 01/17/2024
The vulnerability identified as CVE-2019-18209 represents a cross-site scripting flaw located within the Etherpad-Lite collaborative editing platform version 1.7.5. This issue specifically affects the template file templates/pad.html and manifests when Internet Explorer fails to properly encode URL paths, creating an exploitable condition that allows malicious actors to inject arbitrary script code into web pages viewed by other users. The vulnerability stems from insufficient input validation and output encoding mechanisms within the application's template processing system, where user-supplied data flows directly into the HTML output without proper sanitization. This particular weakness is classified under CWE-79 as a Cross-Site Scripting vulnerability, which is one of the most prevalent and dangerous web application security flaws. The issue demonstrates how browser-specific behavior differences can create unexpected security gaps, as the vulnerability only manifests in Internet Explorer due to its particular handling of URL encoding mechanisms.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious URL containing script code within the path component that gets rendered unescaped in the pad.html template. When Internet Explorer processes this malformed URL, it fails to properly encode the path portion, allowing the injected script to execute within the context of the victim's browser session. This creates a persistent threat vector where attackers can execute malicious JavaScript code, potentially stealing session cookies, redirecting users to malicious sites, or performing actions on behalf of authenticated users. The vulnerability is particularly concerning because Etherpad-Lite is commonly used for collaborative document editing in enterprise environments, making it a valuable target for attackers seeking to compromise sensitive information shared through collaborative platforms.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable more sophisticated attack vectors including session hijacking, data exfiltration, and privilege escalation within the collaborative environment. Attackers could leverage this flaw to gain unauthorized access to shared documents, manipulate collaborative content, or establish persistent backdoors within organizations that rely on Etherpad-Lite for their document management workflows. The vulnerability affects the integrity and confidentiality of collaborative editing sessions, potentially exposing sensitive business information, intellectual property, or personal data that users expect to be secure within the platform. Organizations using this version of Etherpad-Lite face significant risk of data breaches and unauthorized access to their collaborative workspaces, especially in environments where multiple users share common documents and editing sessions.
Mitigation strategies for CVE-2019-18209 should focus on immediate patching of the Etherpad-Lite application to version 1.7.6 or later, which contains the necessary fixes for the URL encoding and output sanitization issues. Organizations should also implement comprehensive input validation and output encoding measures at the application level, ensuring that all user-supplied data passing through template rendering processes undergoes proper sanitization. Network-level protections such as web application firewalls can provide additional defense-in-depth measures, though they should not be relied upon as the sole solution. Security teams should conduct thorough vulnerability assessments of their Etherpad-Lite deployments and review access controls to minimize the potential impact of exploitation. The remediation process should include monitoring for any signs of exploitation attempts and implementing proper logging mechanisms to detect suspicious URL patterns or script injection attempts. Given the nature of the vulnerability and its relationship to browser-specific encoding behavior, organizations should also consider implementing browser policy controls to standardize client-side behavior across their environments, aligning with best practices for web application security as outlined in the OWASP Top Ten and NIST cybersecurity frameworks.