CVE-2021-39306
📋 TL;DR
A stack buffer overflow vulnerability exists in Realtek RTL8195AM devices when handling oversized authentication challenge text in WEP security mode. This allows remote attackers to potentially execute arbitrary code or cause denial of service. Affected are devices using Realtek RTL8195AM chips with firmware versions before 2.0.10.
💻 Affected Systems
- Realtek RTL8195AM-based devices
- Ameba IoT devices using RTL8195AM
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, allowing attacker to install persistent malware, intercept network traffic, or pivot to other network devices.
Likely Case
Denial of service causing device crashes and network disruption, potentially requiring physical reset or reconfiguration.
If Mitigated
Limited impact with proper network segmentation and WEP disabled, though device remains vulnerable to adjacent network attacks.
🎯 Exploit Status
Exploitation requires sending specially crafted authentication packets to devices with WEP enabled. No authentication needed to trigger the vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.0.10 or later
Vendor Advisory: https://www.amebaiot.com/en/security_bulletin/cve-2021-39306/
Restart Required: Yes
Instructions:
1. Download firmware version 2.0.10 or later from Realtek/Ameba website. 2. Follow device-specific firmware update procedure. 3. Reboot device after update. 4. Verify firmware version is 2.0.10 or higher.
🔧 Temporary Workarounds
Disable WEP Security
allSwitch from WEP to WPA2/WPA3 or disable wireless security entirely if appropriate for the environment.
Network Segmentation
allIsolate affected devices on separate VLANs with strict firewall rules to limit attack surface.
🧯 If You Can't Patch
- Disable WEP security immediately and use WPA2/WPA3 instead
- Isolate affected devices from critical networks using VLANs and firewall rules
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via management interface or console. If version is below 2.0.10 and WEP is enabled, device is vulnerable.Check Version:
Device-specific command varies by implementation. Typically accessed via serial console or web interface.Verify Fix Applied:
Confirm firmware version is 2.0.10 or higher via device management interface or console output.📡 Detection & Monitoring
Log Indicators:
- Multiple authentication failures
- Device crash/reboot logs
- Unusual WEP authentication attempts
Network Indicators:
- Oversized authentication packets to port 67/68 (DHCP) or wireless management frames
- WEP authentication floods
SIEM Query:
source="wireless_controller" AND (event_type="authentication_failure" AND size>threshold) OR (protocol="WEP" AND packet_size>normal)