CVE-2020-27630
📋 TL;DR
CVE-2020-27630 is a vulnerability in Silicon Labs uC/TCP-IP 3.6.0 where TCP Initial Sequence Numbers (ISNs) are generated with insufficient randomness. This allows attackers to predict sequence numbers and hijack TCP sessions, perform man-in-the-middle attacks, or inject malicious data. The vulnerability affects embedded systems and IoT devices using this specific TCP/IP stack version.
💻 Affected Systems
- Silicon Labs uC/TCP-IP
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete network compromise through TCP session hijacking, allowing attackers to intercept, modify, or inject data into communications, potentially leading to full system control in critical infrastructure environments.
Likely Case
TCP session hijacking enabling data interception and manipulation in vulnerable embedded systems, particularly in industrial control systems and IoT devices.
If Mitigated
Limited impact if network segmentation, encryption, and proper access controls prevent attackers from reaching vulnerable systems.
🎯 Exploit Status
Exploitation requires network access to vulnerable systems and knowledge of TCP sequence prediction techniques. The vulnerability is well-documented in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 3.6.1 or later
Vendor Advisory: https://www.silabs.com/support/security-advisories/silabs-sa-2021-001-uc-tcp-ip
Restart Required: Yes
Instructions:
1. Identify affected systems running uC/TCP-IP 3.6.0. 2. Obtain updated firmware from device manufacturer. 3. Apply firmware update to all affected devices. 4. Reboot devices to activate the patch. 5. Verify the update was successful.
🔧 Temporary Workarounds
Network Segmentation
allIsolate vulnerable systems from untrusted networks to limit attack surface
Encryption Enforcement
allRequire TLS/SSL encryption for all TCP communications to prevent session hijacking
🧯 If You Can't Patch
- Implement strict network access controls and firewall rules to limit connections to vulnerable systems
- Deploy intrusion detection systems to monitor for TCP sequence prediction attacks and session hijacking attempts
🔍 How to Verify
Check if Vulnerable:
Check device firmware version and verify if uC/TCP-IP 3.6.0 is present. Consult device manufacturer documentation for version identification.Check Version:
Device-specific command varies by manufacturer. Typically requires accessing device console or management interface.Verify Fix Applied:
Verify firmware version has been updated to uC/TCP-IP 3.6.1 or later. Test TCP connections for proper sequence number randomization.📡 Detection & Monitoring
Log Indicators:
- Unexpected TCP resets
- TCP sequence number anomalies
- Multiple failed connection attempts from same source
Network Indicators:
- TCP packets with predictable sequence numbers
- Suspicious TCP session hijacking patterns
- Unusual traffic patterns to embedded devices
SIEM Query:
source_ip="*" AND (tcp.flags.reset=1 OR tcp.sequence_anomaly=1) AND dest_port IN [common_embedded_ports]🔗 References
- https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
- https://www.forescout.com
- https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/
- https://www.cisa.gov/news-events/ics-advisories/icsa-21-042-01
- https://www.forescout.com
- https://www.forescout.com/resources/numberjack-weak-isn-generation-in-embedded-tcpip-stacks/
