CVE-2025-25299 in CKeditor5
Summary
by MITRE • 02/20/2025
CKEditor 5 is a modern JavaScript rich-text editor with an MVC architecture. During a recent internal audit, a Cross-Site Scripting (XSS) vulnerability was discovered in the CKEditor 5 real-time collaboration package. This vulnerability affects user markers, which represent users' positions within the document. It can lead to unauthorized JavaScript code execution, which might happen with a very specific editor and token endpoint configuration. This vulnerability affects only installations with Real-time collaborative editing enabled. The problem has been recognized and patched. The fix is available in version 44.2.1 (and above). Users are advised to upgrade. There are no known workarounds for this vulnerability.
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Analysis
by VulDB Data Team • 02/20/2025
The vulnerability CVE-2025-25299 represents a cross-site scripting flaw within CKEditor 5's real-time collaboration functionality, specifically targeting the user marker component that tracks participant positions within documents. This issue resides in the MVC architecture of the editor system and demonstrates how collaborative features can introduce security risks when not properly validated. The vulnerability operates through a specific configuration pathway involving editor setup and token endpoint handling, making it particularly insidious as it requires particular environmental conditions to manifest. The flaw stems from inadequate input sanitization of user marker data, allowing malicious actors to inject JavaScript payloads that execute within the context of other users' browsing sessions.
The technical exploitation of this vulnerability occurs within the real-time collaboration package where user markers are rendered and managed. When users interact with collaborative documents, their positions are tracked through marker elements that contain identifying information. The XSS vector emerges when these markers contain unescaped or improperly sanitized content that gets injected into the DOM. This vulnerability maps directly to CWE-79 - Improper Neutralization of Input During Web Page Generation, which specifically addresses cross-site scripting conditions where user-controllable data is not properly escaped before being rendered. The attack requires a specific combination of editor configuration and token endpoint setup, making it less common but still potentially devastating when exploited.
The operational impact of CVE-2025-25299 extends beyond simple script execution, as it can enable attackers to perform session hijacking, data theft, and further escalation attacks within the collaborative environment. In real-time editing scenarios where multiple users interact simultaneously, a successful XSS attack could allow an attacker to manipulate document content, steal user credentials, or redirect users to malicious sites. The vulnerability's scope is limited to installations with real-time collaborative editing enabled, but this restriction does not diminish its potential impact given the widespread adoption of collaborative editing features in enterprise environments. The attack surface is particularly concerning in environments where CKEditor 5 is integrated into content management systems, learning management platforms, or collaborative workspaces where user trust and data integrity are paramount.
Security practitioners should prioritize upgrading to CKEditor 5 version 44.2.1 or higher to remediate this vulnerability, as no effective workarounds exist for the specific XSS condition. The mitigation strategy aligns with ATT&CK technique T1566.001 - Phishing: Spearphishing Attachment, as organizations may need to implement additional monitoring for suspicious user marker data or token endpoint configurations. Organizations using CKEditor 5 in collaborative environments should conduct immediate security assessments of their real-time editing implementations and verify that all instances have been updated to the patched version. The vulnerability highlights the importance of validating all user-provided data in collaborative systems and demonstrates how seemingly benign features can become attack vectors when proper input sanitization is not implemented. Given the nature of real-time collaboration, administrators should also consider implementing content security policies and monitoring for anomalous marker data patterns that could indicate exploitation attempts.