A previously undocumented cryptographic implementation vulnerability, codenamed (CVSS 9.8 - Critical), is currently being exploited in the wild. Unlike standard SSH bugs, this flaw allows for pre-authentication command injection specifically when a Cisco device is configured to accept SSHv2 connections with legacy modular exponentiation parameters.
Since Cisco has not yet released a patch, defenders must apply and compensating controls :
Relying purely on configuration workarounds is often insufficient when underlying code contains hard-coded keys or unauthenticated Remote Code Execution (RCE) flaws. Organizations should actively check their inventory for vulnerabilities using official intelligence platforms like the Cisco Security Advisory Central Portal.
Leaked debug logs suggest the flaw resides in the crypto_ssh_kex_cisco_int function—a proprietary Cisco enhancement to the SSH key exchange that handles legacy KEX algorithms (e.g., diffie-hellman-group-exchange-sha1 ). ssh20cisco125 vulnerability exclusive
If you cannot immediately upgrade your hardware or firmware, follow these steps to shield your network:
This vulnerability primarily affects devices running vulnerable versions of: Cisco IOS Software Cisco IOS XE Software
Because many modern automated scanners prioritize newer CVEs, this specific vulnerability often stays hidden in older enterprise networks, industrial control systems (ICS), and edge routers that haven't seen a firmware update in years. It is "exclusive" knowledge because it requires a deep understanding of Cisco’s legacy SSH stack to exploit or even detect manually. The Risk Profile It is "exclusive" knowledge because it requires a
Inbound SSH packets with a TTL of 125 (even if the source IP is only 4 hops away).
# Check if the device is vulnerable output = ssh.exec_command('show version')[0].read().decode() if '12.2(25)' in output or '12.3(2)' in output: print(f"host is VULNERABLE to SSH-2-Cisco-1.25") else: print(f"host is NOT VULNERABLE to SSH-2-Cisco-1.25")
In some variations, attackers can bypass RSA-based public key authentication entirely. 4. Affected Products and data transfer.
Before diving into the vulnerability, it's crucial to have a basic understanding of SSH (Secure Shell). SSH is a cryptographic network protocol used for secure command-line, login, and data transfer. It is commonly used by system administrators to manage remote servers. SSH provides a secure channel over an insecure network, ensuring that the communication between the client and server is encrypted and protected against eavesdropping, hijacking, and other forms of tampering.
: If the scanner encounters a legacy prompt, it automatically feeds precompiled dictionary lists containing default combinations like user cisco and password cisco125 .
Vulnerabilities are often reachable because the VTY lines (virtual terminals) are open to the entire network. 2. Audit SSH and Privilege Settings