CVE-2021-24441
📋 TL;DR
This CSV injection vulnerability in the Sign-up Sheets WordPress plugin allows attackers to embed malicious formulas in exported CSV files. When opened in spreadsheet applications like Excel, these formulas could execute arbitrary commands or leak data. WordPress sites using vulnerable versions of this plugin are affected.
💻 Affected Systems
- Sign-up Sheets WordPress plugin
📦 What is this software?
Sign Up Sheets by Fetchdesigns
⚠️ Risk & Real-World Impact
Worst Case
Attackers could execute arbitrary commands on victim's computer when they open a malicious CSV file, potentially leading to full system compromise, data theft, or ransomware deployment.
Likely Case
Attackers trick users into opening CSV files containing malicious formulas that could execute commands, steal credentials, or exfiltrate data from the victim's spreadsheet application.
If Mitigated
With proper user awareness training and spreadsheet security settings, the impact is limited to potential data manipulation within the spreadsheet application itself.
🎯 Exploit Status
Exploitation requires user interaction (opening the CSV file) and appropriate permissions to create/modify sheet titles. CSV injection techniques are well-documented and easy to implement.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.0.14
Vendor Advisory: https://wpscan.com/vulnerability/ec9292b1-5cbd-4332-bdb6-2351c94f5ac6
Restart Required: No
Instructions:
1. Log into WordPress admin panel. 2. Navigate to Plugins → Installed Plugins. 3. Find 'Sign-up Sheets' plugin. 4. Click 'Update Now' if update is available. 5. Alternatively, download version 1.0.14+ from WordPress repository and manually update.
🔧 Temporary Workarounds
Disable CSV Export
allTemporarily disable CSV export functionality in plugin settings or restrict access to users who need it.
Input Sanitization Filter
allAdd custom WordPress filter to sanitize sheet titles before CSV generation.
add_filter('dls_sus_sheet_title', 'sanitize_text_field');
🧯 If You Can't Patch
- Implement strict user permissions - only allow trusted administrators to create/modify sheet titles
- Educate users about the risks of opening CSV files from untrusted sources and configure spreadsheet applications to disable automatic formula execution
🔍 How to Verify
Check if Vulnerable:
Check WordPress admin → Plugins → Installed Plugins → Sign-up Sheets version. If version is below 1.0.14, you are vulnerable.Check Version:
wp plugin list --name='Sign-up Sheets' --field=versionVerify Fix Applied:
After updating, verify plugin version is 1.0.14 or higher. Test CSV export functionality with special characters in sheet titles to ensure proper sanitization.📡 Detection & Monitoring
Log Indicators:
- Unusual CSV export activity, multiple failed export attempts, or suspicious sheet title modifications
Network Indicators:
- CSV file downloads containing formula characters (=, +, -, @) in content
SIEM Query:
source="wordpress" AND (event="csv_export" OR plugin="sign-up-sheets") AND (title CONTAINS "=" OR title CONTAINS "+" OR title CONTAINS "-" OR title CONTAINS "@")