CVE-2025-22602 in Discourse
Summary
by MITRE • 02/04/2025
Discourse is an open source platform for community discussion. In affected versions an attacker can execute arbitrary JavaScript on users' browsers by posting a malicious video placeholder html element. This issue only affects sites with CSP disabled. This problem has been patched in the latest version of Discourse. Users are advised to upgrade. Users unable to upgrade should enable CSP.
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Analysis
by VulDB Data Team • 09/26/2025
CVE-2025-22602 represents a critical cross-site scripting vulnerability within the Discourse community discussion platform that allows remote attackers to execute arbitrary JavaScript code in users' browsers through malicious video placeholder HTML elements. This vulnerability specifically targets installations where Content Security Policy (CSP) is disabled, making it particularly dangerous for organizations that have not implemented proper web application security controls. The flaw resides in how Discourse processes and renders video placeholder elements, which can be manipulated by attackers to inject malicious script code that executes within the context of legitimate user sessions.
The technical implementation of this vulnerability stems from inadequate input validation and sanitization of HTML content within Discourse's video embedding functionality. When users post content containing malicious video placeholders, the platform fails to properly escape or validate the HTML attributes and content, allowing attackers to inject script tags or other malicious payloads. This issue directly maps to CWE-79 - Improper Neutralization of Input During Web Page Generation, which addresses the failure to properly sanitize user-provided data before it is rendered in web pages. The vulnerability demonstrates how insecure handling of rich text content can lead to full client-side compromise when proper security controls are absent.
The operational impact of CVE-2025-22602 extends beyond simple script execution, potentially enabling attackers to perform session hijacking, data exfiltration, and other malicious activities that compromise user privacy and platform integrity. Given that this vulnerability only affects installations without CSP protection, it underscores the critical importance of implementing comprehensive web application security measures. Organizations running Discourse without proper CSP headers become vulnerable to sophisticated attacks that can persistently compromise user sessions and access sensitive community data. The vulnerability aligns with ATT&CK technique T1566.001 - Phishing: Spearphishing Attachment, as attackers can leverage this flaw to deliver malicious payloads through seemingly legitimate community discussions.
Mitigation strategies for this vulnerability include immediate upgrading to the patched version of Discourse, which addresses the core sanitization issues in the HTML processing pipeline. For organizations unable to upgrade immediately, enabling Content Security Policy headers with appropriate restrictions provides effective protection against script injection attacks. The recommended CSP implementation should include directives such as 'script-src' with strict source controls and 'object-src' restrictions to prevent execution of embedded content. Additionally, organizations should implement proper input validation for all user-generated content, particularly rich text fields, and consider implementing additional security layers such as web application firewalls to detect and prevent exploitation attempts. The vulnerability serves as a reminder that web applications must implement defense-in-depth strategies to protect against various attack vectors, particularly when dealing with user-generated content in community platforms.