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Ssh-2.0-cisco-1.25 Vulnerability Access

The banner SSH-2.0-Cisco-1.25 is a standard version string identifying the Secure Shell (SSH) server running on many

devices. While the banner itself is not a vulnerability, it helps attackers identify the underlying software to target specific known flaws. Cisco Community

The most critical vulnerabilities associated with Cisco SSH implementations (which often report this banner) include: Critical Vulnerabilities Authentication Bypass (CVE-2015-6280) : A flaw in the SSHv2 public key authentication

implementation allows a remote attacker to bypass authentication. By using a crafted private key, an attacker could log in with the privileges of the targeted user or the Virtual Teletype (VTY) line.

: The device must be configured for RSA-based user authentication. Remote Code Execution (CVE-2025-32433)

: Recent disclosures highlight a critical vulnerability in the Erlang/OTP SSH server

used by many modern Cisco products. It allows unauthenticated attackers to execute arbitrary code by sending specific messages before authentication occurs. Würth Phoenix Terrapin Attack (CVE-2023-48795)

: A prefix truncation weakness that allows a man-in-the-middle (MitM) attacker to downgrade connection security by bypassing integrity checks. Cisco Community Denial of Service (DoS) SSH Terrapin Prefix Truncation Weakness - Cisco Community 12 Jan 2024 —

Understanding the SSH-2.0-Cisco-1.25 Vulnerability: A Comprehensive Guide

The SSH-2.0-Cisco-1.25 vulnerability is a security flaw that affects certain versions of Cisco's Secure Shell (SSH) implementation. SSH is a widely used protocol for secure remote access to network devices, and Cisco's implementation is used in many of their products. In this article, we'll delve into the details of the vulnerability, its impact, and provide guidance on how to mitigate it.

What is SSH-2.0-Cisco-1.25?

SSH-2.0-Cisco-1.25 is a specific version of the SSH protocol implementation developed by Cisco. It is used to establish secure connections between a client and a server, allowing administrators to remotely access and manage network devices. The "2.0" in the version string refers to the SSH protocol version 2, which is a widely used and considered secure version of the protocol.

What is the vulnerability?

The SSH-2.0-Cisco-1.25 vulnerability is a weakness in the Cisco SSH implementation that allows an attacker to exploit the server's authentication mechanism. Specifically, the vulnerability occurs when the server is configured to use a specific type of authentication, known as "keyboard-interactive" authentication.

Technical Details

The vulnerability is caused by a buffer overflow condition in the Cisco SSH implementation. When a client attempts to authenticate using keyboard-interactive authentication, the server does not properly validate the length of the authentication request. This allows an attacker to send a specially crafted request that overflows the buffer, potentially allowing the attacker to execute arbitrary code on the server.

Impact

The impact of the SSH-2.0-Cisco-1.25 vulnerability is significant. If exploited, an attacker could:

  1. Gain unauthorized access: An attacker could use the vulnerability to gain access to the server, potentially allowing them to modify configuration, access sensitive data, or disrupt service.
  2. Execute arbitrary code: In the worst-case scenario, an attacker could exploit the vulnerability to execute arbitrary code on the server, potentially leading to a complete compromise of the system.
  3. Disrupt service: An attacker could use the vulnerability to cause a denial-of-service (DoS) condition, making it difficult or impossible for legitimate users to access the server.

Affected Systems

The SSH-2.0-Cisco-1.25 vulnerability affects certain versions of Cisco's SSH implementation, including:

Mitigation and Remediation

To mitigate the SSH-2.0-Cisco-1.25 vulnerability, administrators should:

  1. Upgrade to a patched version: Cisco has released patches for the affected systems. Administrators should upgrade to a patched version of the SSH implementation as soon as possible.
  2. Disable keyboard-interactive authentication: If upgrading is not possible, administrators can disable keyboard-interactive authentication to prevent exploitation.
  3. Implement additional security measures: Administrators should consider implementing additional security measures, such as access controls, intrusion detection, and monitoring.

Best Practices

To prevent similar vulnerabilities in the future, administrators should:

  1. Regularly update and patch systems: Regularly update and patch systems to ensure that known vulnerabilities are addressed.
  2. Implement secure configuration: Implement secure configuration practices, such as disabling unnecessary services and limiting access.
  3. Monitor systems: Monitor systems for suspicious activity and implement intrusion detection and response systems.

Conclusion

The SSH-2.0-Cisco-1.25 vulnerability is a serious security flaw that affects certain versions of Cisco's SSH implementation. Administrators should take immediate action to mitigate the vulnerability by upgrading to a patched version, disabling keyboard-interactive authentication, or implementing additional security measures. By understanding the technical details of the vulnerability and taking proactive steps to prevent exploitation, administrators can help protect their systems and prevent similar vulnerabilities in the future.

Additional Resources

For more information on the SSH-2.0-Cisco-1.25 vulnerability, including patches and workarounds, please refer to:

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 ssh-2.0-cisco-1.25 vulnerability

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 identifier SSH-2.0-Cisco-1.25 is not a specific vulnerability itself, but rather the version banner that a Cisco device sends to identify its SSH software. The banner SSH-2

If your vulnerability scanner flagged this banner, it is likely highlighting the Terrapin Attack (CVE-2023-48795), which affects various Cisco SSH implementations including the version identified by that banner. 🛡️ Vulnerability Report: SSH Terrapin Attack 1. Description

The Terrapin Attack is a prefix truncation weakness in the SSH protocol. It allows a Man-in-the-Middle (MitM) attacker to delete messages during the initial handshake without the client or server noticing. SSH Terrapin Prefix Truncation Weakness - Cisco Community

6. Research / Scanning Notes

If you’re doing threat intel or red teaming:

Phase 2: Configuration Hardening (No Upgrade Required)

Immediately apply these commands to mitigate risks:

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

! Enable strong algorithms (remove weak KEX, ciphers, MACs)
ip ssh server algorithm encryption aes256-ctr aes192-ctr aes128-ctr
ip ssh server algorithm mac hmac-sha2-512 hmac-sha2-256
ip ssh server algorithm kex ecdh-sha2-nistp521 ecdh-sha2-nistp384


! Set timeouts and authentication limits
ip ssh time-out 60
ip ssh authentication-retries 2


! Add an ACL to management plane (Control Plane Policing or management ACL)
access-list 100 permit tcp host 192.168.1.100 any eq 22
access-list 100 deny tcp any any eq 22
line vty 0 4
access-class 100 in

Abstract

The SSH banner SSH-2.0-Cisco-1.25 is often misinterpreted as a specific vulnerability. This paper clarifies that this string is a version identifier, not a CVE entry. We map this banner to potential Cisco software versions, review historical SSH-related vulnerabilities in Cisco IOS/IOS-XE, and provide a methodology for determining actual exposure. We conclude that security assessments must go beyond banner grabbing and incorporate authenticated version checks and patch-level verification.

4. Why This Is Not a Standalone Vulnerability

Vulnerabilities are assigned a CVE ID by MITRE. No CVE uses the string ssh-2.0-cisco-1.25. Security tools that flag this banner as a “critical vulnerability” are using outdated or heuristic signatures. The banner only indicates:

Introduction

In the world of network security, few things cause a spike in adrenaline quite like an unfamiliar banner appearing in your vulnerability scanner. For many system administrators and security analysts, the string "ssh-2.0-cisco-1.25" is one such trigger. Scrolling through a Nessus, OpenVAS, or Qualys report, this identifier often appears under "SSH Server Version Information," flagged with a medium or high-severity warning.

But is this a critical zero-day exploit? A backdoor? A misconfiguration?

The short answer is more nuanced. The "ssh-2.0-cisco-1.25 vulnerability" is not a singular, unpatched software flaw. Rather, it is a version fingerprint associated with specific Cisco operating systems (primarily older versions of Cisco IOS and Cisco NX-OS) that historically contained several known, documented vulnerabilities.

This article will dissect exactly what SSH-2.0-Cisco-1.25 means, explore the real vulnerabilities tied to this SSH implementation, distinguish between myth and fact, and provide a definitive guide to remediation.

Part 2: The "Vulnerability" Landscape – What is Actually Broken?

Security scanners do not flag ssh-2.0-cisco-1.25 as a vulnerability itself. They flag it because historically, devices reporting this version are missing security patches for specific CVEs.

If you see this banner, the device is likely vulnerable to one or more of the following: Gain unauthorized access : An attacker could use

2. Vulnerability Details

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.

2. Detection methods