Ssh-2.0-cisco-1.25 Vulnerability [better] -

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

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 ssh-2.0-cisco-1.25 vulnerability

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 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

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

Identification: An SSH banner reveals implementation and version hints. Tools and scanners use banners to classify devices, prioritize targets, and infer known vulnerabilities.
Fingerprinting risk: Even absent an exploit, a banner like "SSH-2.0-Cisco-1.25" makes it trivial for an observer to identify Cisco gear running certain SSH stacks. That reduces an attacker’s reconnaissance cost.
False comfort: Administrators sometimes assume “only the banner” is harmless. In practice, banner exposure plus other metadata can accelerate automated attacks.

The real vulnerabilities behind similar banners

Banner ≠ vulnerability, but it can correlate to real bugs. Cisco SSH implementations historically carried several serious issues — from RSA-based auth bypasses to state-machine or exceptional-condition handling that enabled DoS (e.g., CVE entries involving Cisco SSH implementations). Attackers don’t need a novel zero-day if a known CVE maps to the disclosed implementation.
Resource exhaustion and state-machine flaws are subtle. Some Cisco SSH flaws let an authenticated or semi-authenticated actor craft specific traffic patterns to crash or reload devices. Those are not the flashy remote code executions, but they can cause network-wide outages.

Operational trade-offs

Hiding versus hardening: Removing or editing SSH banners reduces fingerprinting but is defensive theater if the underlying software remains vulnerable. Hardening (patching, minimizing exposure, strict auth, rate-limiting, network segmentation) provides substantive protection.
Attack surface beyond SSH: Banner disclosure often correlates with other detectable services and outdated software; attackers use aggregated signals. Treat banner information as one of many telemetry cues, not an isolated problem.

Practical, prioritized actions

Patch proactively: Treat advisories for SSH implementations seriously. Even DoS-class CVEs can have high operational impact.
Minimize exposure: Limit SSH to management networks, enforce ACLs, MFA where feasible, and restrict source IPs.
Disable weak auth methods: Remove legacy/unsupported SSH auth schemes and disable unused protocol versions.
Rate-limit and monitor: Apply connection-rate controls and monitor for suspicious connect patterns indicative of exploitation attempts.
Consider banner control as part of defense-in-depth: If your platform supports safe banner changes, reducing obvious fingerprinting is a low-cost additional layer — but never a substitute for patches and access controls.

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.

6. References

CVE-2015-5665: SSH Denial of Service vulnerability.
CVE-2015-4000: Logjam Attack (Diffie-Hellman Key Exchange).
NIST SP 800-131A: Transitioning the Use of Cryptographic Algorithms and Key Lengths.
Cisco Security Advisories: Cisco Security Vulnerability Policy

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.

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

5. Remediation

Short-term:

Restrict SSH access via ACLs (management interface only).
Disable weak KEX/ciphers if possible (rare on very old IOS).

Long-term:

Upgrade IOS to a fixed release (e.g., 15.2(4)E or 15.9(3)M).
Migrate to IOS-XE if hardware supports it.
Replace EOL hardware.

Example fixed banner after upgrade:

SSH-2.0-Cisco-2.22   (IOS 15.9)
SSH-2.0-Cisco-2.36   (IOS-XE 16.x)

Part 7: Frequently Asked Questions

Q: Is ssh-2.0-cisco-1.25 a virus or malware? A: No. It is a version banner. However, it indicates the device is likely missing security patches, making it a prime target for malware or ransomware.

Q: Can I hide the banner to pass a scan? A: Yes, via ip ssh version and ip ssh server algorithm commands, plus changing the login banner. But this is "security by obscurity." A determined attacker will still probe for vulnerabilities.

Q: Does this affect Cisco Meraki or new Catalyst 9000 series? A: No. Modern Cisco platforms run a completely different SSH stack (often based on OpenSSH) and report different version strings (e.g., SSH-2.0-Cisco-2.0 or SSH-2.0-OpenSSH_8.2).

Q: Is there a known exploit code available? A: Yes. Public Metasploit modules and Python scripts exist for CVE-2009-2879 (DoS) and downgrade attacks. Always verify any exploit in a lab before testing on production.

Part 3: Vulnerability Assessment – Is It a False Positive?

Security practitioners often argue whether reports of ssh-2.0-cisco-1.25 are "false positives."

Technically: The scanner is correct. The device does run that version.
Contextually: Is the device exposed to the internet? If it is an internal access switch with no public IP, the risk of remote exploitation is minimized. However, internal threats (malware, disgruntled employees) still exist.
Functionally: A device may have had its SSH version string manually changed (e.g., via ip ssh version 2 and ip ssh server algorithm tuning) but still reports the old banner. Configuration registers can hide the true patch status.

The golden rule: Do not ignore the finding. Treat it as a signal to investigate, not as a confirmed exploit.

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.

Phase 4: Continuous Monitoring

Deploy SNMP traps for SSH login failures.
Use NetFlow to detect anomalous SSH connection attempts.
Re-scan quarterly with credentialed vulnerability scans (not just banner grabs).

What is `ssh-2.0-cisco-1.25`?

When an SSH client connects to a server, the server sends a "banner" identifying its software version. In this case, the string breaks down as follows:

SSH-2.0: The device supports SSH protocol version 2.
Cisco-1.25: This indicates the specific software implementation running on a Cisco device.

The version "1.25" is archaic. It dates back to early Cisco IOS (Internetwork Operating System) implementations from the early-to-mid 2000s. While modern Cisco devices run much newer SSH implementations, seeing this specific version string in 2023/2024 is an immediate red flag. It suggests the device is running an operating system that has not been updated in potentially two decades.