CVE-2021-21777
📋 TL;DR
CVE-2021-21777 is a critical out-of-bounds read vulnerability in the Ethernet/IP UDP handler of OpENer EtherNet/IP stack. Attackers can send specially crafted network packets to read sensitive memory contents from affected devices. This affects industrial control systems and IoT devices using vulnerable versions of the OpENer stack.
💻 Affected Systems
- EIP Stack Group OpENer EtherNet/IP Stack
📦 What is this software?
Opener by Opener Project
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise leading to information disclosure of sensitive data, potential credential theft, and possible remote code execution through memory corruption.
Likely Case
Information disclosure of adjacent memory contents, potentially exposing sensitive data, configuration details, or authentication tokens.
If Mitigated
Limited information disclosure with proper network segmentation and access controls in place.
🎯 Exploit Status
Exploitation requires sending specially crafted UDP packets to port 44818 (EtherNet/IP). Proof-of-concept code is publicly available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 2.4 or later
Vendor Advisory: https://github.com/EIPStackGroup/OpENer/releases
Restart Required: Yes
Instructions:
1. Update OpENer stack to version 2.4 or later. 2. Recompile any applications using the stack. 3. Restart affected services or devices.
🔧 Temporary Workarounds
Network Segmentation
allIsolate EtherNet/IP devices from untrusted networks
Firewall Rules
linuxBlock UDP port 44818 from untrusted sources
iptables -A INPUT -p udp --dport 44818 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate EtherNet/IP devices
- Deploy intrusion detection systems to monitor for exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check if OpENer version is 2.3 or includes commit 8c73bf3. Review application dependencies for vulnerable stack version.Check Version:
Check application documentation or build configuration for OpENer versionVerify Fix Applied:
Verify OpENer version is 2.4 or later. Check that applications have been recompiled with patched stack.📡 Detection & Monitoring
Log Indicators:
- Unusual UDP traffic on port 44818
- Memory access violation logs
- Application crash logs
Network Indicators:
- Malformed UDP packets to port 44818
- Unusual outbound traffic from EtherNet/IP devices
SIEM Query:
source_port=44818 AND (packet_size>normal OR malformed_packet=TRUE)