CVE-2024-40626
📋 TL;DR
This is a stored cross-site scripting (XSS) vulnerability in Outline's document editor that allows authenticated users to inject malicious JavaScript into documents. When other users view these documents, the JavaScript executes within Outline's origin, potentially compromising user sessions and data. The vulnerability is particularly dangerous in self-hosted deployments where file storage shares the same domain as Outline, allowing CSP bypass.
💻 Affected Systems
- Outline
📦 What is this software?
Outline by Getoutline
⚠️ Risk & Real-World Impact
Worst Case
An attacker could steal authentication tokens, hijack user sessions, perform actions as authenticated users, exfiltrate sensitive document data, or deploy ransomware within the Outline environment.
Likely Case
Attackers with authenticated access could embed malicious scripts in documents to steal session cookies, redirect users to phishing sites, or perform limited actions within the compromised user's context.
If Mitigated
With proper CSP rules and separate domains for file storage, the attack surface is reduced, but authenticated users could still execute limited JavaScript within document contexts.
🎯 Exploit Status
Exploitation requires authenticated user access to create malicious documents. The advisory provides technical details but no public exploit code.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.77.3
Vendor Advisory: https://github.com/outline/outline/security/advisories/GHSA-888c-mvg8-v6wh
Restart Required: Yes
Instructions:
1. Backup your Outline instance and database. 2. Update to version 0.77.3 or later using your deployment method (Docker, manual, etc.). 3. Restart the Outline service. 4. Verify the update was successful.
🔧 Temporary Workarounds
No official workarounds
allThe vendor states there are no known workarounds for this vulnerability.
🧯 If You Can't Patch
- Restrict document creation and editing permissions to trusted users only
- Implement Content Security Policy with strict directives and separate file storage domain
🔍 How to Verify
Check if Vulnerable:
Check your Outline version via the admin interface or by inspecting the application metadata. If version is below 0.77.3, you are vulnerable.Check Version:
Check the Outline admin dashboard or inspect the application's HTTP headers for version information.Verify Fix Applied:
Confirm the Outline version is 0.77.3 or higher in the admin interface or application metadata.📡 Detection & Monitoring
Log Indicators:
- Unusual document creation patterns
- Multiple users accessing the same malicious document
- JavaScript errors in browser console logs
Network Indicators:
- Unexpected outbound connections from Outline to external domains
- Large data exfiltration from document viewing sessions
SIEM Query:
Search for document creation events followed by multiple user access events within short timeframes, or look for base64-encoded JavaScript in document content.