CVE-2020-23356
📋 TL;DR
This vulnerability allows attackers to bypass authentication in Nibbleblog by exploiting PHP type juggling. Attackers can log in as any user without valid credentials by submitting specially crafted password hashes. This affects all Nibbleblog installations running vulnerable versions.
💻 Affected Systems
- Nibbleblog
📦 What is this software?
Nibbleblog by Nibbleblog
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the blog system allowing attackers to gain administrative access, modify content, upload malicious files, and potentially pivot to other systems.
Likely Case
Unauthorized access to the blog administration panel leading to content manipulation, defacement, or data theft.
If Mitigated
Limited impact with proper network segmentation and monitoring, though authentication bypass remains possible.
🎯 Exploit Status
The vulnerability is simple to exploit with publicly available proof-of-concept code. Attackers only need to send specially crafted login requests.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in GitHub repository via pull request #148
Vendor Advisory: https://github.com/dignajar/nibbleblog/pull/148
Restart Required: No
Instructions:
1. Download the patched login.class.php file from the GitHub pull request. 2. Replace the vulnerable file at /admin/kernel/api/login.class.php. 3. No restart required as PHP files are interpreted on each request.
🔧 Temporary Workarounds
Temporary code modification
linuxManually edit the vulnerable file to replace '==' with '===' for password hash comparison
sed -i "s/\$password_hash == \$user_hash/\$password_hash === \$user_hash/g" /path/to/admin/kernel/api/login.class.php
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block authentication bypass attempts
- Restrict access to the admin interface using IP whitelisting or VPN requirements
🔍 How to Verify
Check if Vulnerable:
Check if login.class.php contains '==' comparison for password hashes instead of '==='Check Version:
Check Nibbleblog version in configuration files or admin panelVerify Fix Applied:
Verify that login.class.php now uses '===' for password hash comparisons📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts with unusual hash values
- Successful logins from unexpected IP addresses
Network Indicators:
- HTTP POST requests to login endpoint with specially crafted password parameters
SIEM Query:
source="web_logs" AND (uri_path="/admin/index.php" OR uri_path="/admin/kernel/api/login.class.php") AND (status=200 OR status=302) AND user_agent NOT IN ["expected_user_agents"]