CVE-2018-8879
📋 TL;DR
This is a critical stack-based buffer overflow vulnerability in ASUS router firmware that allows remote attackers to execute arbitrary code by sending specially crafted long strings to the blocking.asp page. It affects ASUS routers running Asuswrt-Merlin firmware older than 384.4 and ASUS firmware before 3.0.0.4.382.50470.
💻 Affected Systems
- ASUS routers with Asuswrt-Merlin firmware
- ASUS routers with stock ASUS firmware
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router with remote code execution, allowing attackers to intercept traffic, pivot to internal networks, install persistent malware, or brick the device.
Likely Case
Router takeover leading to man-in-the-middle attacks, credential theft, DNS hijacking, and network surveillance.
If Mitigated
Limited impact if patched, with only denial of service possible if other protections are bypassed.
🎯 Exploit Status
Exploitation requires sending HTTP requests with long parameters to blocking.asp, which is trivial to automate.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Asuswrt-Merlin 384.4+, ASUS firmware 3.0.0.4.382.50470+
Vendor Advisory: https://www.asus.com/Networking/RTAC66U/HelpDesk_BIOS
Restart Required: Yes
Instructions:
1. Log into router admin interface. 2. Navigate to firmware update section. 3. Download latest firmware from ASUS support site. 4. Upload and apply firmware update. 5. Reboot router.
🔧 Temporary Workarounds
Disable remote administration
allPrevents external attackers from accessing the vulnerable web interface.
Restrict admin interface access
allLimit access to router admin interface to trusted IP addresses only.
🧯 If You Can't Patch
- Isolate vulnerable routers in separate network segments with strict firewall rules
- Implement network monitoring for suspicious HTTP requests to blocking.asp with long parameters
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under System Log or Administration section.Check Version:
Login to router web interface and navigate to System Information or similar status page.Verify Fix Applied:
Confirm firmware version is Asuswrt-Merlin 384.4+ or ASUS firmware 3.0.0.4.382.50470+.📡 Detection & Monitoring
Log Indicators:
- HTTP requests to /blocking.asp with unusually long flag, mac, or cat_id parameters
- Multiple failed buffer overflow attempts in system logs
Network Indicators:
- HTTP GET/POST requests to router IP on port 80/443 with long parameter strings
- Unusual traffic patterns from router after compromise
SIEM Query:
http.url:*blocking.asp* AND (http.param.length>100 OR http.request_length>500)