CVE-2021-3693
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in LedgerSMB that allows attackers to inject malicious HTML fragments into the DOM. When exploited, it can lead to remote code execution and information disclosure. The vulnerability affects authenticated users who can be tricked into visiting specially crafted URLs.
💻 Affected Systems
- LedgerSMB
📦 What is this software?
Ledgersmb by Ledgersmb
Ledgersmb by Ledgersmb
Ledgersmb by Ledgersmb
Ledgersmb by Ledgersmb
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, and lateral movement within the network.
Likely Case
Session hijacking, credential theft, and unauthorized access to sensitive financial data within LedgerSMB.
If Mitigated
Limited impact with proper input validation and output encoding, potentially reduced to minor information disclosure.
🎯 Exploit Status
Exploitation requires social engineering to trick authenticated users into clicking malicious links. The vulnerability is well-documented with public proof-of-concept available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.8.0 and later
Vendor Advisory: https://ledgersmb.org/cve-2021-3693-cross-site-scripting
Restart Required: Yes
Instructions:
1. Backup your LedgerSMB database and configuration files. 2. Download LedgerSMB version 1.8.0 or later from the official repository. 3. Follow the upgrade instructions at https://ledgersmb.org/upgrading. 4. Restart the web server and LedgerSMB services.
🔧 Temporary Workarounds
Input Validation Filter
allImplement server-side input validation to sanitize HTML fragments before DOM insertion
# Requires custom code modification - implement proper HTML sanitization in affected endpoints
Content Security Policy
allImplement strict Content Security Policy headers to restrict script execution
# Add to web server configuration: Content-Security-Policy: default-src 'self'; script-src 'self'
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block malicious HTML injection patterns
- Restrict access to LedgerSMB to trusted networks only and implement strict authentication controls
🔍 How to Verify
Check if Vulnerable:
Check LedgerSMB version - if it's below 1.8.0, the system is vulnerable. Review application logs for suspicious URL patterns containing HTML/script tags.Check Version:
Check the LedgerSMB admin interface or review the application's version file in the installation directoryVerify Fix Applied:
Verify LedgerSMB version is 1.8.0 or later. Test that HTML injection attempts are properly sanitized and do not execute.📡 Detection & Monitoring
Log Indicators:
- Unusual URL patterns containing script tags or HTML fragments in access logs
- Multiple failed authentication attempts followed by successful login
Network Indicators:
- HTTP requests containing malicious script payloads in URL parameters
- Outbound connections to suspicious domains from the LedgerSMB server
SIEM Query:
source="ledgersmb_access.log" AND (url="*<script>*" OR url="*javascript:*" OR url="*onload=*" OR url="*onerror=*")🔗 References
- https://huntr.dev/bounties/daf1384d-648a-43fd-9b35-5c37d8ead667
- https://ledgersmb.org/cve-2021-3693-cross-site-scripting
- https://www.debian.org/security/2021/dsa-4962
- https://huntr.dev/bounties/daf1384d-648a-43fd-9b35-5c37d8ead667
- https://ledgersmb.org/cve-2021-3693-cross-site-scripting
- https://www.debian.org/security/2021/dsa-4962
