Ssh-2.0-cisco-1.25 Vulnerability May 2026
An attacker sending a single crafted SSHv2 packet can crash the device. No logs may be left before crash.
The vulnerability fingerprint disappears only when you upgrade to a patched Cisco IOS/NX-OS release.
After upgrade, verify the new banner (which should be something like SSH-2.0-Cisco-2.0 or SSH-2.0-Cisco-1.99).
Based on the format Cisco-1.25, the device likely dates to the mid-2000s. Common SSH vulnerabilities in that era include:
| CVE ID | Description | Affected Versions (Example) | |--------|-------------|-----------------------------| | CVE-2007-1242 | SSH v1 buffer overflow (legacy) | Cisco IOS 12.2-12.4 | | CVE-2010-0567 | SSH v2 memory corruption | Cisco IOS 12.2(25) series | | CVE-2015-6294 | SSH key exchange algorithm downgrade | Cisco IOS-XE 3.13S |
Note: Cisco-1.25 alone does not confirm any specific CVE. It must be cross-referenced with show version output.
On Cisco ASA devices that reported similar version strings (often overlapping with 1.25), there was a vulnerability where processing specific SSH packets would not free memory correctly. Over days or weeks, the device would exhaust memory and stop passing traffic. This required a reboot to resolve.
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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
Vulnerability Alert: SSH-2.0-Cisco-1.25
Overview
The SSH-2.0-Cisco-1.25 vulnerability is a security flaw in the Secure Shell (SSH) protocol implementation on certain Cisco devices. This vulnerability can allow an attacker to gain unauthorized access to the device, potentially leading to a compromise of the system's confidentiality, integrity, and availability.
Affected Devices
The vulnerability affects Cisco devices running SSH-2.0-Cisco-1.25, which is a specific implementation of the SSH protocol on Cisco IOS and IOS XE devices.
Vulnerability Details
The SSH-2.0-Cisco-1.25 vulnerability is caused by a weakness in the way the SSH protocol handles authentication requests. An attacker can exploit this vulnerability by sending a specially crafted SSH packet to the device, which can cause the device to crash or allow the attacker to gain unauthorized access.
Exploitation
An attacker can exploit this vulnerability using the following methods: ssh-2.0-cisco-1.25 vulnerability
Risk Level
The risk level of this vulnerability is considered High, as it can allow an attacker to gain unauthorized access to the device and potentially compromise the system's confidentiality, integrity, and availability.
Mitigation and Remediation
To mitigate and remediate this vulnerability, Cisco has released patches and workarounds. The recommended solutions are:
Cisco Advisory
Cisco has released an advisory to address this vulnerability, which can be found at: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191106-ssh-1
References
Conclusion
The SSH-2.0-Cisco-1.25 vulnerability is a serious security flaw that can allow an attacker to gain unauthorized access to Cisco devices. It is essential to take immediate action to mitigate and remediate this vulnerability to prevent potential exploitation.
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 identifier SSH-2.0-Cisco-1.25 is not a specific vulnerability itself, but rather the SSH banner string that many Cisco IOS and IOS XE devices use to identify their software version during an SSH handshake. When vulnerability scanners flag this string, they are typically reporting that the device is susceptible to a broader protocol-level flaw, most commonly the Terrapin Attack (CVE-2023-48795). What is the SSH-2.0-Cisco-1.25 "Vulnerability"?
The appearance of this string in security reports usually indicates the device is running a version of Cisco software that has not yet been hardened against recent SSH exploits. There are two primary security concerns currently associated with this banner: 1. The Terrapin Attack (CVE-2023-48795)
This is a prefix truncation attack that targets the SSH protocol's integrity. CSCwi61646 - SSH Terrapin Prefix Truncation ... - Cisco Bug
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.
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
The string SSH-2.0-Cisco-1.25 is not a vulnerability itself, but rather the software version banner identifying a Cisco device's SSH service. Because this banner reveals the specific vendor and version, security scanners often flag it to suggest checking for known vulnerabilities associated with Cisco's SSH implementation.
The most critical contemporary vulnerability associated with Cisco SSH services is the Terrapin attack (CVE-2023-48795), which affects various Cisco platforms including Catalyst switches and XR routers. Key Vulnerabilities for Cisco SSH
While SSH-2.0-Cisco-1.25 identifies the service, the following actual vulnerabilities are often what scanners are warning about: Edit banner SSH-2.0-Cisco-1.25
Hello, Is possible to edit the default message SSH-2.0-Cisco-1.25 ?? ... Labels: NGFW Firewalls. Cisco Community
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. An attacker sending a single crafted SSHv2 packet
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.
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
The string SSH-2.0-Cisco-1.25 is not a specific vulnerability itself, but rather the version banner
that a Cisco device sends when a connection is initiated over port 22. Cisco Community
While the banner is a standard part of the SSH handshake, it is frequently flagged by security scanners (like Nessus or Qualys) as "potentially vulnerable" because it reveals that the device is running an older or specific version of the Cisco SSH server. Cisco Community Understanding the Banner : Indicates the device is using SSH Protocol Version 2.0. Cisco-1.25
: This is the internal version of the Cisco SSH software implementation. Cisco Community Why Scanners Flag This
Security tools often alert on this banner because it helps attackers perform fingerprinting
—identifying the exact operating system and software version to find matching exploits. Several critical vulnerabilities have affected Cisco devices running versions associated with this banner over the years: NetCom Learning SSH Terrapin Prefix Truncation Weakness - Cisco Community
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": After upgrade, verify the new banner (which should
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 string SSH-2.0-Cisco-1.25 SSH server banner typically seen when connecting to Cisco IOS or IOS-XE devices. This banner itself is a version string, not a specific vulnerability, but its presence indicates the device is running a version of the Cisco SSH implementation that may be susceptible to several known protocol-level and implementation-specific vulnerabilities. Devolutions Forum Key Vulnerabilities Associated with Cisco SSH
If your device reports this version string, it may be affected by the following vulnerabilities depending on the specific software release (IOS/IOS-XE): RSA-Based Authentication Bypass (CVE-2015-6280)
: A flaw in the SSHv2 public key authentication implementation could allow a remote attacker to bypass user authentication by using a crafted private key. This requires the attacker to know a valid username and the corresponding public key. SSH Denial of Service (CVE-2020-3200)
: A vulnerability in the SSH state machine of Cisco IOS and IOS-XE Software could allow an authenticated, remote attacker to cause the device to reload by sending a specific traffic pattern, leading to a Denial of Service (DoS). Terrapin Attack (CVE-2023-48795)
: A prefix truncation weakness in the SSH protocol that could allow a man-in-the-middle attacker to downgrade the connection's security by deleting messages from the beginning of the secure channel. Erlang SSH Remote Code Execution (RCE)
: Recent reports in April 2025 highlight a critical RCE vulnerability in the Erlang-based SSH server used in some Cisco product lines. This is a "Perfect 10" severity flaw that allows unauthenticated code execution. Cisco Community How to Verify and Mitigate SSH Terrapin Prefix Truncation Weakness - Cisco Community
The identifier "SSH-2.0-Cisco-1.25" is not a standard CVE (Common Vulnerabilities and Exposures) number, but rather a specific SSH banner string observed on some older Cisco devices.
This banner typically indicates a Cisco device running an outdated SSH server implementation (likely from an older IOS release). The actual vulnerability most often associated with this banner is CVE-2011-1322 (and related issues like CVE-2009-4408), which concerns a weakness in Cisco’s SSH v2 implementation.
Below is a practical guide to understanding, detecting, and mitigating the risk.
If you’re doing threat intel or red teaming:
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 —
This is a classic vulnerability found in Cisco IOS versions that shipped with SSH-2.0-Cisco-1.25. A crafted SSHv2 packet could cause the device to reload. The attack required only a single TCP connection and did not need authentication. An unauthenticated, remote attacker could crash a core router or switch, causing a network-wide outage. CVSS Score: 7.8 (High)
