Vulnerability: Ssh-2.0-cisco-1.25

If you are required to submit this as a formal paper for academic or professional use, I strongly recommend that you:

Would you like me to help you instead:

If an immediate software upgrade is not possible due to hardware limitations, apply the following configurations on the Cisco device:

Devices reporting ssh-2.0-cisco-1.25 often default to outdated Key Exchange (Kex) algorithms, such as diffie-hellman-group1-sha1. This algorithm uses a 768-bit prime modulus, which is computationally feasible to break with sufficient resources (e.g., a nation-state or well-funded attacker). Modern standards require 2048-bit (group14) or higher.

The "ssh-2.0-cisco-1.25 vulnerability" is not a single bug but rather a historical signature of neglect. It tells a story: a Cisco device deployed years ago, likely stable, and forgotten by security teams. While the banner itself does not guarantee compromise, it dramatically increases the attack surface.

Your path forward is clear:

In cybersecurity, the loudest alarms often lead to the oldest problems. ssh-2.0-cisco-1.25 is your network’s way of telling you that yesterday’s configuration cannot defend against tomorrow’s attacks. Listen to it.

This article is for educational and defensive purposes. Always verify vulnerabilities against Cisco’s official PSIRT (Product Security Incident Response Team) advisories before taking action.

The phrase "SSH-2.0-Cisco-1.25" is a standard identification banner sent by many Cisco devices when a remote connection is initiated. While the banner itself is not a vulnerability, it acts as a "fingerprint" that tells attackers exactly what version of the Cisco SSH software is running, which helps them target specific known flaws.

Currently, the "story" for this version involves two major security concerns: 1. The Terrapin Attack (CVE-2023-48795)

Many Cisco devices using the Cisco-1.25 SSH stack were found to be vulnerable to the Terrapin attack.

The Flaw: This is a "prefix truncation" attack where a man-in-the-middle (MitM) attacker can secretly remove parts of the encrypted handshake.

The Impact: By removing these early messages, an attacker can downgrade your connection's security, turning off modern encryption features or security extensions without the user ever knowing.

Fix: Cisco has released bug fixes (e.g., CSCwi61646 for Catalyst switches) that implement a "strict key exchange" to block this attack. 2. Critical Remote Code Execution (CVE-2025-32433)

In early 2025, a critical vulnerability was identified in certain Cisco products where the SSH server was built using the Erlang/OTP library. ssh-2.0-cisco-1.25 vulnerability

The Flaw: An attacker can send specific protocol messages before authenticating, exploiting a memory or logic error in how the SSH server handles early communication.

The Impact: This is a 10.0 CVSS (Maximum Severity) flaw because it allows an unauthenticated attacker to execute code remotely (RCE) on the device, potentially taking full control.

Status: While this affects many devices showing the Cisco-1.25 banner, it specifically impacts those running the Erlang-based SSH service. Summary of Risk Exposure

Over 300,000 devices globally were recently detected online with this specific banner. Main Vulnerabilities Terrapin Attack (Downgrade) and Pre-Auth RCE. Mitigation

Update your Cisco IOS/NX-OS to the latest version. You can check your status on the Cisco Bug Search Tool using your specific device model.

CSCwi64420 - SSH vulnerable to terrapin attack ... - Cisco Bug

SSH-2.0-Cisco-1.25 — a banner string that shows up when an SSH client probes a Cisco device — reads like a tiny mechanical signature, but it’s also an entry point into wider questions about security, disclosure, and how small protocol details can have outsized effects.

Why that banner matters

The real vulnerabilities behind similar banners

Operational trade-offs

Practical, prioritized actions

A final thought That modest string—SSH-2.0-Cisco-1.25—is both a fingerprint and a narrative warp: it encapsulates how tiny protocol disclosures change attacker economics and how seemingly small implementation quirks cascade into real-world outages. Security that treats banners as trivia misses the larger lesson: resilience comes from reducing exposure, fixing root causes, and assuming attackers will connect the dots.

The string SSH-2.0-Cisco-1.25 is not a specific vulnerability itself, but rather the software version banner

that a Cisco device displays when you connect to its SSH server. If you are required to submit this as

Security scanners (like Nessus or Qualys) often flag this banner because it reveals the device's operating system and version, which can help an attacker identify known vulnerabilities. Below is a breakdown of what this banner means and the actual vulnerabilities often associated with it. What is SSH-2.0-Cisco-1.25?

When an SSH client connects to a Cisco router or switch, the two devices exchange "version strings" to ensure they can talk to each other.

: Indicates the device is using SSH protocol version 2.0 (more secure than 1.x). Cisco-1.25

: This is the specific internal version of the Cisco SSH server software running on the device. Why do scanners flag it? (The "Vulnerability")

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

. By advertising the exact version of the SSH server, the device tells a potential attacker exactly which bugs might be exploitable on that specific system.

However, "Cisco-1.25" is found across many different IOS versions. Depending on which IOS version you are running, your device might be vulnerable to several real, documented threats: SSH Terrapin Prefix Truncation Weakness - Cisco Community

Here’s a breakdown of what’s commonly referred to in security research as the “SSH-2.0-Cisco-1.25” fingerprint, including its background, associated vulnerabilities, and how to investigate it properly.

Final note: There is no separate “SSH-2.0-Cisco-1.25” CVE. Treat this banner as a red flag indicating you should verify your device’s IOS version against historical Cisco SSH DoS vulnerabilities. If you need the exact fixed IOS version for your hardware, provide the full show version output.

Understanding the "SSH-2.0-Cisco-1.25" Banner and Modern Security Risks

If you have recently run a vulnerability scan like Nessus or OpenVAS against your Cisco infrastructure, you may have seen a reference to SSH-2.0-Cisco-1.25. While this string is actually a version banner rather than a single specific "vulnerability," it often serves as a primary indicator for several critical security flaws affecting Cisco’s SSH implementation. What is SSH-2.0-Cisco-1.25?

This is a software banner identifying the SSH server running on your Cisco device. SSH-2.0: Indicates the device is running SSH Version 2.

Cisco-1.25: Refers to a specific legacy version of the Cisco SSH stack found in various Cisco IOS, IOS XE, and older PIX/ASA software releases.

Because this version is dated, it is frequently flagged by scanners because it supports weak cryptographic algorithms or is susceptible to protocol-level attacks discovered in recent years. Top Vulnerabilities Linked to This Version Would you like me to help you instead:

When security professionals discuss the "Cisco-1.25 vulnerability," they are typically referring to one of the following critical issues: 1. The Terrapin Attack (CVE-2023-48795)

Many Cisco devices running the 1.25 stack are vulnerable to the Terrapin attack, a prefix truncation weakness.

The Risk: A Man-in-the-Middle (MitM) attacker can downgrade the connection's security by deleting specific protocol messages during the handshake without the client or server noticing. Cisco Bug ID: CSCwi61646. 2. Unauthenticated Remote Code Execution (CVE-2025-32433)

Recent advisories have highlighted a maximum-severity flaw (CVSS 10.0) in certain Cisco SSH implementations (specifically those utilizing Erlang/OTP libraries).

The Risk: Attackers can execute arbitrary code on the target system without needing to authenticate first.

Affected Banner: This has been observed in environments reporting the SSH-2.0-Cisco-1.25 banner. 3. Weak Cryptographic Algorithms

Older Cisco SSH stacks often default to algorithms now considered "broken" or "weak":

KEX Algorithms: Support for diffie-hellman-group1-sha1 or diffie-hellman-group-exchange-sha1.

Ciphers: Continued use of CBC-mode ciphers (e.g., aes128-cbc), which are susceptible to side-channel attacks. How to Secure Your Cisco Device

If your scanner has flagged this banner, follow these steps to mitigate the risk: Step 1: Update Your IOS/IOS XE Software

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

If you cannot upgrade immediately, manually disable weak algorithms in the CLI:

# Disable weak Diffie-Hellman groups ip ssh dh min size 2048 # Specify secure ciphers (prefer CTR or GCM modes) ip ssh server algorithm encryption aes256-ctr aes192-ctr aes128-ctr # Specify secure Message Authentication Codes (MACs) ip ssh server algorithm mac hmac-sha2-256 hmac-sha2-512 Use code with caution. Copied to clipboard Step 3: Obfuscate the Banner (Optional)

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 Terrapin (CVE-2023-48795) 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.

Are you seeing this alert on a specific model, like a Catalyst switch or an ASA firewall? Providing the hardware type can help narrow down the exact patch you need.

The identification of Cisco-1.25 suggests the device is utilizing an older SSH implementation library. Below are the primary vulnerabilities associated with this specific banner.