Ssh-2.0-cisco-1.25 Vulnerability [updated] Here

! Disable SSHv1 entirely no ip ssh version 1 ip ssh version 2

The string is a version identifier frequently returned by the Secure Shell (SSH) server on Cisco IOS and IOS XE devices during a protocol handshake. While this specific string describes the Cisco implementation of the SSH-2.0 protocol rather than a single vulnerability, devices reporting this version have recently been linked to a maximum-severity flaw (CVSS 10.0) in the underlying Erlang/OTP SSH server implementation. The Critical Erlang/OTP SSH Vulnerability

The string ssh-2.0-cisco-1.25 is more than just a version number; it is a marker of technical debt. It represents a time capsule of security weaknesses that have long since been solved. In an era of automated ransomware and sophisticated state-sponsored attacks, leaving such a device exposed is an invitation for disaster. Network administrators must prioritize the identification and remediation of these legacy systems to maintain the integrity of their infrastructure. ssh-2.0-cisco-1.25 vulnerability

While not a security control, altering the default SSH banner can reduce the effectiveness of automated reconnaissance tools. This can be accomplished by configuring a custom login banner that is sent before authentication. However, it is important to note that experienced attackers can still fingerprint the device using other techniques, and this should never be considered a primary security measure.

When a client initiates an SSH connection to a device, the two systems exchange software version strings. This process is called banner grabbing. The string breaks down as follows: : The device uses SSH version 2.0. The Critical Erlang/OTP SSH Vulnerability The string ssh-2

(Not ideal – SSHv1 is insecure.)

If an immediate patch is not possible, temporarily disable RSA-based authentication on the VTY lines. line vty 0 15 no ip ssh pubkey-chain Use code with caution. Cisco announced CVE-2025-20159

1. The Core Vulnerabilities Associated with SSH-2.0-Cisco-1.25

In 2025, Cisco announced CVE-2025-20159, a critical vulnerability affecting the management interface ACL processing in Cisco IOS XR Software. This vulnerability allows an unauthenticated, remote attacker to completely bypass configured access control lists (ACLs) for SSH, NetConf, and gRPC features. This is a severe failure because management ACLs are intended to be the last line of defense, restricting which IP addresses can reach the device's management plane. A bypass renders these access rules completely ineffective.

Certain legacy Cisco SSH implementations suffer from memory leaks or CPU exhaustion flaws when bombarded with malformed packets or crafted key exchange requests.

⚠️ is widely exploited in 1.25 today, but DoS and downgrade attacks are still possible.