Ssh-2.0-cisco-1.25 Vulnerability [2021] Jun 2026

Certain historic deployments of Cisco-1.25 lack strict cryptographic path validation when utilizing RSA keys for administrator access.

These historical issues illustrate a clear trend: the SSH-2.0-Cisco stack, while functional, has been a persistent source of risk, often requiring software updates to resolve.

: An attacker continuously floods port 22 with unusual or malformed SSH requests.

Legacy operational technology (OT) environments fear downtime more than security. A router that controls a pipeline cannot be rebooted for a patch without a maintenance window that may not exist for months. ssh-2.0-cisco-1.25 vulnerability

: The authentication step is entirely bypassed. The attacker gains immediate terminal access matching the elevated privileges of the target VTY lines. 4. Denial of Service (DoS) Through Resource Exhaustion

For network security professionals, the appearance of this banner should trigger an immediate and focused investigation. The priority must be on upgrading the software, enforcing strict access controls, and implementing defense-in-depth strategies. While the banner itself is not a "vulnerability," it is a signal that the device's SSH implementation is outdated and out of step with modern security requirements. In an era where nation-state actors actively target Cisco infrastructure with zero-day exploits, ignoring this signal is a risk no organization can afford to take.

show version | include IOS show ip ssh

To determine if SSH-2.0-Cisco-1.25 indicates a vulnerable device:

First, you must know which of your devices are running the SSH-2.0-Cisco-1.25 banner or similar vulnerable implementations. Network scanners and configuration management tools can help.

Addressing the risks associated with devices displaying the SSH-2.0-Cisco-1.25 banner requires a multi-layered approach, combining immediate tactical fixes with long-term strategic upgrades. Certain historic deployments of Cisco-1

! Example Access Control List access-list 10 permit 192.168.10.5 line vty 0 4 access-class 10 in transport input ssh Use code with caution. Conclusion

! Example Configuration Hardening ip ssh server algorithm encryption aes128-ctr aes192-ctr aes256-ctr ip ssh server algorithm mac hmac-sha2-256 hmac-sha2-512 ip ssh server algorithm kex diffie-hellman-group14-sha256 Use code with caution. 4. Implement Strict Access Control

The string SSH-2.0-Cisco-1.25 is parsed into two distinct parts: The attacker gains immediate terminal access matching the

: If an environment has RSA public-key authentication configured , an attacker who discovers a valid local username can gain shell access with the underlying privileges assigned to that terminal line. 2. Device Reload and Denial of Service (CVE-2020-3200)