Ssh-2.0-cisco-1.25 Vulnerability !!install!!

: An unauthenticated remote attacker initiates an SSH session using public-key authentication and forces a parsing exception.

The most effective fix is to upgrade to a modern, patched version of Cisco software. Check the Cisco Security Advisory for your specific hardware to find the recommended "Gold Star" release. Step 2: Harden the SSH Configuration

The string breaks down into distinct components. The "SSH-2.0" prefix indicates that the server supports version 2.0 of the SSH protocol. The "Cisco" label identifies the vendor's proprietary implementation. The "1.25" suffix represents the internal version number of Cisco's SSH server code, not the version of the IOS operating system itself. This server version was particularly prevalent on devices running older software trains, where SSH functionality was often treated as a separate software component rather than a deeply integrated feature.

: Under specific, highly structured traffic patterns, the software's internal SSH state machine fails to resolve out-of-sequence errors correctly. ssh-2.0-cisco-1.25 vulnerability

While "security by obscurity" isn't a primary defense, you can prevent casual scanning from identifying your exact version. On some platforms, you can customize or suppress parts of the SSH banner via the banner command, though the protocol-level version string (Cisco-1.25) is often hard-coded into the stack. Summary Table Vulnerability Mitigation Security Downgrade Disable ChaCha20-Poly1305 and CBC ciphers. RCE (CVE-2025-32433) Full System Takeover Immediate software update/patching. Weak KEX/Ciphers Data Decryption Update ip ssh settings to use SHA-2 and CTR.

Security tools often alert on this banner because it helps attackers perform fingerprinting

If you cannot upgrade immediately, manually disable weak algorithms in the CLI: : An unauthenticated remote attacker initiates an SSH

This article provides a comprehensive overview of what this signature means, why it is considered a vulnerability, the potential risks involved, and how to mitigate it effectively as of 2026. What is SSH-2.0-Cisco-1.25?

The string SSH-2.0-Cisco-1.25 is parsed into two distinct parts:

If it connects without warning → vulnerable. Step 2: Harden the SSH Configuration The string

On supported devices, the SSH configuration should be hardened to disable all weak and deprecated cryptographic primitives. This includes explicitly disabling key exchange algorithms like diffie-hellman-group1-sha1 , which are commonly required for compatibility with older devices. Administrators should also disable older protocol versions and weaker cipher suites where possible.

The most severe threat associated with this service profile involves an unauthenticated bug stemming from the Erlang/OTP SSH layer.

When an SSH client connects to a server, the server sends a "banner" identifying its software version. In this case, the string breaks down as follows:

Upgrade to a fixed IOS version: