CVE-2022-31561
📋 TL;DR
This vulnerability allows attackers to perform absolute path traversal attacks in the varijkapil13/Sphere_ImageBackend repository, enabling unauthorized access to sensitive files on the server. It affects users who deployed this Flask-based image backend software before the 2019-10-03 commit. The vulnerability stems from unsafe use of Flask's send_file function without proper path validation.
💻 Affected Systems
- varijkapil13/Sphere_ImageBackend
📦 What is this software?
Sphere Imagebackend by Sphere Imagebackend Project
⚠️ Risk & Real-World Impact
Worst Case
Complete server compromise with arbitrary file read access, potentially exposing sensitive configuration files, credentials, and system files leading to full system takeover.
Likely Case
Unauthorized access to application files, configuration data, and potentially sensitive user data stored on the server filesystem.
If Mitigated
Limited impact with proper file system permissions, web server sandboxing, and input validation preventing traversal attempts.
🎯 Exploit Status
Path traversal vulnerabilities are well-understood and easily weaponized with simple HTTP requests containing directory traversal sequences.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions after 2019-10-03 commit
Vendor Advisory: https://github.com/github/securitylab/issues/669#issuecomment-1117265726
Restart Required: Yes
Instructions:
1. Update to latest version from GitHub repository
2. Verify the send_file function now includes proper path validation
3. Restart the Flask application server
🔧 Temporary Workarounds
Input Validation Middleware
allAdd middleware to validate and sanitize all file path inputs before processing
# Add path validation in Flask route handlers
import os
from werkzeug.utils import safe_join
# Replace direct send_file calls with:
def safe_send_file(path):
base_dir = '/safe/base/directory'
safe_path = safe_join(base_dir, path)
if safe_path is None or not safe_path.startswith(base_dir):
return 'Invalid path', 400
return send_file(safe_path)
Web Server Sandboxing
linuxConfigure web server to run in chroot jail or container with restricted filesystem access
# For systemd services:
[Service]
ReadWritePaths=/var/www/html
ReadOnlyPaths=/etc/nginx
PrivateTmp=yes
ProtectSystem=strict
# For Docker:
docker run -v /safe/path:/app/data:ro your_image
🧯 If You Can't Patch
- Implement strict file system permissions limiting web server user to only necessary directories
- Deploy WAF rules to block path traversal patterns (../, absolute paths) in HTTP requests
🔍 How to Verify
Check if Vulnerable:
Test by sending HTTP requests with path traversal sequences to image endpoints (e.g., GET /image?file=../../../etc/passwd) and checking if sensitive files are returned.Check Version:
Check git commit history or repository version: git log --oneline | grep -i '2019-10-03'Verify Fix Applied:
Attempt the same path traversal attacks after patching; they should return error responses instead of file contents.📡 Detection & Monitoring
Log Indicators:
- HTTP requests containing '../' sequences
- Access to files outside expected image directories
- 404 errors for expected image files followed by successful file reads
Network Indicators:
- HTTP requests with encoded path traversal sequences (%2e%2e%2f)
- Unusual file extensions in image requests
- Requests for known sensitive files (passwd, shadow, config files)
SIEM Query:
source="web_logs" AND (url="*../*" OR url="*/etc/*" OR url="*/proc/*" OR url="*/sys/*") AND response_code=200