Ssh-2.0-cisco-1.25 Vulnerability Jun 2026

The SSHredder test suite revealed multiple critical flaws:

Devices exposing this banner generally span several generations of Cisco software, making them vulnerable to several critical flaws depending on the exact implementation.

Furthermore, security tools actively detect these vulnerabilities. For instance, Tenable's Nessus has plugins ( 165676 , 94070 , 209660 ) that check for the denial-of-service flaw (CSCvx63027), the NX-OS command execution (CVE-2015-0721), and the ASA command injection (CVE-2024-20329) across various Cisco platforms.

: The module mishandles invalid or malformed RSA keys during the validation phase. ssh-2.0-cisco-1.25 vulnerability

A significant vulnerability in the SSH version 2 protocol implementation allows unauthenticated, remote attackers to bypass user authentication. To exploit this, an attacker must know a valid username configured for RSA-based authentication.

Older Cisco SSH implementations, including those that may return the 1.25 identifier, have been subject to other notable security advisories: What is Cisco-1.25 in ssh logging.

This signature breaks down into three key functional components: The SSHredder test suite revealed multiple critical flaws:

This banner serves as a highly reliable fingerprinting tool. Automated vulnerability scanners, including Nessus, actively parse these banners to determine the operating system and potential vulnerability set of a target. OS guessing tools like Exscript have hardcoded routines that directly map the banner SSH-2.0-Cisco-1.25 to the Cisco IOS operating system.

The string is not a specific flaw itself, but rather the standardized software banner broadcasted by the Cisco IOS SSH server to establish cryptographic handshakes. Because this exact string maps to hundreds of thousands of active Enterprise routing and switching environments, threat actors look for this specific banner to identify target networks for a range of Cisco IOS and IOS XE SSH protocol flaws.

: The device runs into an unhandled exception state and triggers a forced system reload, generating a sustained Denial of Service (DoS) window across the production environment. 3. RSA-Based Public Key Authentication Bypass : The module mishandles invalid or malformed RSA

Security audits often list this as a "medium" or "low" risk because of Information Disclosure

Vulnerabilities related to SSH host key validation have also been identified. CVE-2025-20163 in the Cisco Nexus Dashboard Fabric Controller (NDFC) allows an unauthenticated, remote attacker to impersonate NDFC-managed devices. The flaw is due to insufficient SSH host key validation, which enables a machine-in-the-middle (MitM) attack. An attacker in a position to intercept network traffic could capture and decrypt SSH sessions meant for the legitimate device.

By combining software updates with strict configuration hardening, you can successfully protect your infrastructure from exploits targeting legacy Cisco SSH versions.

The SSH-2.0-Cisco-1.25 vulnerability can have significant consequences, including: