The most common critical finding for this specific version is the preference for the Diffie-Hellman Group 1 (diffie-hellman-group1-sha1) key exchange.
Use nmap script:
nmap --script ssh2-enum-algos -p 22 <target>
nmap --script ssh-hostkey --script-args ssh_hostkey=all -p 22 <target>
Look for:
Upgrade to a fixed IOS version:
Check Cisco’s advisory for your exact hardware and feature set.
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
The “Cisco-1.25” likely refers to an internal version tag used in Cisco’s SSH implementation. This may correspond to:
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 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.
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
The string "SSH-2.0-Cisco-1.25" is a version identifier frequently returned by the Secure Shell (SSH) server on Cisco IOS and IOS XE devices during a protocol handshake. While this specific string describes the Cisco implementation of the SSH-2.0 protocol rather than a single vulnerability, devices reporting this version have recently been linked to a maximum-severity flaw (CVSS 10.0) in the underlying Erlang/OTP SSH server implementation. The Critical Erlang/OTP SSH Vulnerability
In April 2025, a critical vulnerability was disclosed affecting the Erlang/OTP SSH server, which is embedded in various Cisco products and telecommunications systems. ssh-2.0-cisco-1.25 vulnerability
Severity: Classified with a CVSS v3.1 score of 10.0, indicating maximum severity.
Mechanism: The flaw exists in the handling of SSH protocol messages during the authentication phase. An unauthenticated, remote attacker can send specific connection protocol messages before authentication is completed.
Impact: A successful exploit allows for unauthenticated remote code execution (RCE) on the target system. This can lead to full system compromise, including unauthorized data access and denial of service (DoS).
Exploitation: Cisco’s Product Security Incident Response Team (PSIRT) noted attempted exploitation of this vulnerability in the wild as of June 2025. Exposure and Attack Surface
Security research reports from April 2025 highlighted significant global exposure for devices identifying as "SSH-2.0-Cisco-1.25". Shodan: Approximately 92,000 exposed instances found. Censys: Over 103,000 instances identified. FOFA: Up to 309,000 instances detected. Related Historical Vulnerabilities
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.
0 Helpful. Georg Pauwen. VIP Alumni. 02-16-2021 12:30 AM. Hello, I think the '1.25' part is the Cisco specific vendor version ID. Cisco Community SSH Terrapin Prefix Truncation Weakness - Cisco Community
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 —
Security Report: SSH-2.0-Cisco-1.25 Vulnerability
Introduction
The SSH-2.0-Cisco-1.25 vulnerability is a security issue affecting Cisco devices that use the Secure Shell (SSH) protocol for secure remote access. This report provides an overview of the vulnerability, its impact, and recommendations for mitigation.
Vulnerability Details
The SSH-2.0-Cisco-1.25 vulnerability is a known issue in the Cisco SSH implementation, specifically in the SSH-2.0-Cisco-1.25 software. This vulnerability allows an attacker to potentially exploit the SSH protocol and gain unauthorized access to the device.
Technical Details
Vulnerability Description
The SSH-2.0-Cisco-1.25 vulnerability is caused by a buffer overflow in the SSH protocol implementation. An attacker can exploit this vulnerability by sending a specially crafted SSH packet to the device, which can lead to:
Impact
The SSH-2.0-Cisco-1.25 vulnerability can have significant consequences, including:
Mitigation and Recommendations
To mitigate the SSH-2.0-Cisco-1.25 vulnerability:
Conclusion
The SSH-2.0-Cisco-1.25 vulnerability is a serious security issue that requires immediate attention. By understanding the vulnerability and taking steps to mitigate it, organizations can protect their Cisco devices and prevent potential security breaches.
Recommendations for Future Actions
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
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) The most common critical finding for this specific
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.
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:
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:
Best Practices
To prevent similar vulnerabilities in the future, administrators should:
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:
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.