SSH
Vulnerability
Cryptography
SSH Vulnerable to Downgrade Attack
ThreatMate Team
Dec 2023
3 min read
The Download
Security researchers have disclosed a vulnerability in SSH implementations that allows attackers to force a downgrade to weaker cryptographic algorithms. This "Terrapin" attack affects the SSH protocol itself.
The attack exploits vulnerabilities (CVE-2023-48795, CVE-2023-46445, CVE-2023-46446) to downgrade the security of OpenSSH connections.
Understanding the Risk
The SSH protocol is used universally for secure remote access. The discovered vulnerability allows a man-in-the-middle attacker to:
- Force the connection to use weaker encryption
- Potentially decrypt sensitive session data
- Inject commands into the SSH session
Mitigation Steps
- Update SSH software — Apply patches immediately
- Disable weak ciphers — Configure SSH to only allow strong cipher suites
- Monitor for unusual activity — Watch for SSH connections using deprecated algorithms
- Network segmentation — Limit SSH access to trusted networks
Configuration Example
Add to your sshd_config:
Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com
MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.comReady to secure your attack surface?
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