CVE-2019-11887
📋 TL;DR
This vulnerability in SimplyBook.me allows attackers to upload malicious files without proper restrictions, potentially leading to remote code execution. Any SimplyBook.me instance running through May 11, 2019 is affected, allowing attackers to take control of the system.
💻 Affected Systems
- SimplyBook.me
📦 What is this software?
Simplybook by Simplybook
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to execute arbitrary code, steal data, deploy ransomware, or pivot to other systems.
Likely Case
Attackers upload web shells or malicious scripts to gain persistent access, deface websites, or steal sensitive booking data.
If Mitigated
With proper file upload restrictions and validation, impact is limited to potential file storage abuse without code execution.
🎯 Exploit Status
File upload vulnerabilities are commonly exploited and weaponized. The high CVSS score suggests exploitation is straightforward.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 2019-05-11
Vendor Advisory: https://news.simplybook.me/notification/
Restart Required: No
Instructions:
1. Log into SimplyBook.me admin panel
2. Check current version
3. If version is 2019-05-11 or earlier, upgrade to latest version
4. Verify file upload functionality is properly restricted
🔧 Temporary Workarounds
File Upload Restriction
allImplement strict file type validation and size limits on all file upload endpoints
Implement server-side validation for allowed file extensions (e.g., only .jpg, .png, .pdf)
Set maximum file size limits
Scan uploaded files for malicious content
Web Application Firewall Rules
allBlock suspicious file upload patterns and executable file types
Configure WAF to block uploads of .php, .asp, .jsp, .exe files
Set rules to detect base64 encoded payloads in uploads
Monitor for unusual file upload patterns
🧯 If You Can't Patch
- Disable all file upload functionality in the application
- Implement network segmentation to isolate the vulnerable system from critical assets
🔍 How to Verify
Check if Vulnerable:
Check SimplyBook.me version in admin panel. If version date is 2019-05-11 or earlier, system is vulnerable.Check Version:
Check admin dashboard or contact SimplyBook.me support for version informationVerify Fix Applied:
After patching, attempt to upload a test file with executable extension. Verify it is rejected with proper error message.📡 Detection & Monitoring
Log Indicators:
- Unusual file uploads with executable extensions
- Multiple failed upload attempts followed by successful suspicious upload
- Web shell access patterns in access logs
Network Indicators:
- HTTP POST requests to upload endpoints with unusual file types
- Traffic to newly created suspicious URLs after uploads
SIEM Query:
source="web_logs" AND (uri="*upload*" OR uri="*file*" OR method="POST") AND (file_ext="php" OR file_ext="asp" OR file_ext="jsp" OR file_ext="exe")