Ssh-2.0-cisco-1.25 Vulnerability ((hot)) (2026 Edition)

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) ssh-2.0-cisco-1.25 vulnerability

: 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 —

The identifier "SSH-2.0-Cisco-1.25" is a software version string returned by the SSH banner on many Cisco IOS-based devices. While not a specific vulnerability name itself, this version string is frequently associated with several critical security flaws that affect the SSH implementation in Cisco IOS and IOS XE software. Notable Vulnerabilities Associated with Cisco SSH

Security researchers and automated scanners often flag devices displaying this banner because they may be susceptible to the following high-impact issues:

Authentication Bypass (CVE-2015-0923): 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.

Denial of Service (CVE-2020-3200): A flaw in the SSH server code allows an authenticated remote attacker to cause a device reload. This occurs due to an internal state machine error that can be triggered by specific traffic patterns, leading to a DoS condition.

Remote Code Execution (CVE-2025-32433): Recent reports have identified a critical vulnerability (CVSS 10.0) in certain Cisco products using the Erlang/OTP SSH implementation. It allows unauthenticated remote code execution by sending connection protocol messages before authentication occurs. The banner SSH-2

Resource Exhaustion: Older Cisco IOS releases using SSH with TACACS+ authentication are vulnerable to resource exhaustion, which can lead to spontaneous reloads. Scope and Exposure

Scanning tools like Shodan and Censys have identified over 100,000 exposed instances globally of the "SSH-2.0-Cisco-1.25" banner. This broad exposure makes these devices prime targets for automated exploit scripts. Remediation and Best Practices

Cisco has released software updates to address these vulnerabilities across its product lines. Administrators are advised to:

Upgrade Firmware: Consult the Cisco Security Advisories page to identify the fixed release for your specific hardware.

Restrict Management Access: Use Access Control Lists (ACLs) to limit SSH access to known, trusted management IP addresses.

Disable Vulnerable Features: If immediate patching is not possible, consider temporarily disabling RSA-based public key authentication if it is the primary vector for a known bypass. CVE-2020-3200 Detail - NVD Example: SSH-2

Part 5: Step-by-Step Remediation and Hardening

If you have identified devices reporting ssh-2.0-cisco-1.25, follow this prioritized action plan.

1. Introduction

Network scanning tools like Nmap or Shodan frequently report banners such as SSH-2.0-Cisco-1.25. Penetration testers and security analysts may mistakenly search for a “CVE-XXXX-XXXX” matching this exact string. This paper corrects that misconception and provides a practical framework for risk assessment.

2. Banner Interpretation

The SSH protocol begins with a server identification string (RFC 4253, section 4.2):

SSH-<protocol version>-<software version> <comments>

Example: SSH-2.0-Cisco-1.25

• Protocol version: 2.0
• Software version: Cisco-1.25

The “Cisco-1.25” likely refers to an internal version tag used in Cisco’s SSH implementation. This may correspond to:

• Cisco IOS release 12.2(25) series (historically vulnerable to CVE-2007-1242, CVE-2010-0567, etc.)
• A specific SSH server module version embedded in IOS-XE.

1. What is the actual vulnerability?

The core issue is a remotely triggerable denial-of-service (DoS) vulnerability in the SSHv2 implementation of Cisco IOS software. A crafted SSHv2 packet can cause the device to crash or reload.

• CVE-2011-1322: Cisco IOS SSHv2 Denial of Service
• Affected versions: Many Cisco IOS releases from 12.2 through 12.4, and early 15.0, that include the ip ssh version 2 feature.
• Not vulnerable: Devices with SSH disabled, or using only SSHv1.

The banner SSH-2.0-Cisco-1.25 is not a guarantee of vulnerability – it’s an identifier. The real risk depends on the exact IOS version and patch level.