CVE-2020-7248
📋 TL;DR
CVE-2020-7248 is a stack-based buffer overflow vulnerability in libubox's JSON serialization in OpenWrt. It allows remote attackers to execute arbitrary code or cause denial of service by sending specially crafted JSON data. This affects OpenWrt devices running vulnerable versions.
💻 Affected Systems
- OpenWrt
📦 What is this software?
Openwrt by Openwrt
Openwrt by Openwrt
Openwrt by Openwrt
Openwrt by Openwrt
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, allowing attacker to install malware, pivot to internal networks, or create persistent backdoors.
Likely Case
Denial of service causing device crashes and service disruption, potentially requiring physical reset.
If Mitigated
Limited impact if proper network segmentation and input validation are in place, though buffer overflow risk remains.
🎯 Exploit Status
Exploitation requires sending malformed JSON data to services using libubox's JSON serialization. The vulnerability is in a widely used library component.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OpenWrt 18.06.7 and 19.07.1
Vendor Advisory: https://openwrt.org/advisory/2020-01-31-2
Restart Required: Yes
Instructions:
1. Update OpenWrt using opkg package manager: 'opkg update && opkg upgrade' 2. Alternatively, flash firmware to patched versions 18.06.7 or 19.07.1 3. Reboot device after update
🔧 Temporary Workarounds
Disable JSON services
linuxDisable or restrict access to services using libubox JSON serialization if not required
Identify services using libubox: 'ps aux | grep -i libubox'
Disable unnecessary services: '/etc/init.d/service_name stop && /etc/init.d/service_name disable'
Network segmentation
linuxRestrict network access to OpenWrt management interfaces
Add firewall rules: 'uci add firewall rule' with appropriate source/destination restrictions
Apply changes: 'uci commit firewall && /etc/init.d/firewall restart'
🧯 If You Can't Patch
- Isolate affected devices in separate network segments with strict firewall rules
- Implement network monitoring for abnormal JSON traffic patterns to/from OpenWrt devices
🔍 How to Verify
Check if Vulnerable:
Check OpenWrt version: 'cat /etc/openwrt_release' or 'opkg list-installed | grep libubox'Check Version:
cat /etc/openwrt_release | grep VERSIONVerify Fix Applied:
Verify libubox version is patched: 'opkg list-installed libubox' should show version with fix📡 Detection & Monitoring
Log Indicators:
- Segmentation fault or crash logs in /var/log/messages
- Abnormal process termination of services using libubox
Network Indicators:
- Unusual JSON payloads to OpenWrt management interfaces
- Traffic patterns indicating buffer overflow attempts
SIEM Query:
source="openwrt" AND ("segmentation fault" OR "buffer overflow" OR "libubox crash")🔗 References
- https://github.com/openwrt/openwrt/commits/master
- https://nvd.nist.gov/vuln/detail/CVE-2020-7248#range-4512438
- https://openwrt.org/advisory/2020-01-31-2
- https://openwrt.org/advisory/2020-01-31-2
- https://github.com/openwrt/openwrt/commits/master
- https://nvd.nist.gov/vuln/detail/CVE-2020-7248#range-4512438
- https://openwrt.org/advisory/2020-01-31-2
- https://openwrt.org/advisory/2020-01-31-2
