Ssh20cisco125 Vulnerability Info

Note: If you are referring to a specific internal tracking ID, please replace the bracketed details with the correct CVE (e.g., CVE-2024-20399, CVE-2023-20198, or CVE-2024-20412).

1. Generate a Stronger RSA Key (2048-bit minimum)

On the Cisco device:

configure terminal
crypto key zeroize rsa   ! WARNING: This removes all existing RSA keys – do this out-of-hours
crypto key generate rsa modulus 2048

Confirm the new key:

show crypto key mypubkey rsa | include Modulus

Expected: Modulus Length (bits): 2048

Real-world impact scenarios

  • Remote compromise of network devices (routers, switches, firewalls, VPN appliances) leading to:
    • persistent administrative backdoors,
    • traffic interception/manipulation,
    • network-wide lateral movement,
    • loss of confidentiality/integrity for tunneled traffic.
  • Service outages due to crash-inducing exploits.
  • Exposure of private keys or credentials used for automation/configuration.

Vulnerability Context: Cisco WLC SSH Denial of Service (DoS)

Affected Product: Cisco 2500 Series Wireless LAN Controllers (e.g., model 2504) running specific AireOS versions. Protocol: SSHv2 (SSH version 2) Common Search Terms: cisco-sa-20190417-wlc-ssh, CSCvj97874, ssh20cisco125 ssh20cisco125 vulnerability

Why This Isn’t Officially a CVE (Yet)

As of mid-2025, no CVE with ID “SSH20Cisco125” exists. The reason: Most security bodies treat this as misconfiguration rather than a software vulnerability. Cisco has documented since 2010 (Field Notice FN - 63155) that keys under 1024 bits are deprecated. However, many organizations ignored this. The “SSH20Cisco125” label emerged from:

  • Red team internal tools – used as a detection signature.
  • Dark web exploit packs – “Cisco125” is a selling point for botnet controllers targeting industrial control systems (ICS) and legacy SCADA networks using Cisco gear.

Thus, while not a formal CVE, the risk is critical for any network still running these devices. Note: If you are referring to a specific

1. Executive Summary

The identifier SSH-2.0-Cisco125 refers to a specific SSH protocol banner string used by legacy Cisco networking devices (specifically certain Cisco 1200 series Access Points and Wireless Bridges). While often flagged by modern vulnerability scanners as a "vulnerability," this issue is primarily an Information Disclosure weakness.

The presence of this specific banner allows attackers to precisely identify the device model and operating system version. This precise fingerprinting enables attackers to tailor their exploitation strategies using known vulnerabilities associated with the specific hardware or firmware version, such as the Cisco LEAP authentication vulnerability (CVE-2003-1091) or other legacy cryptographic weaknesses. Confirm the new key: show crypto key mypubkey

Impact

  • Primary Effect: Denial of Service (DoS). The SSH process would crash, rendering the management interface unresponsive via SSH.
  • Secondary Effect: In some versions, the entire controller would reload (reboot), causing all connected access points to disassociate and disrupting wireless services.
  • Availability: High impact. Repeated exploitation leads to persistent service interruption.

What Is "SSH20Cisco125"? Decoding the Name

To understand the threat, let’s parse the keyword:

  • SSH20 – Refers to SSH version 2.0, the protocol standard used for secure remote administration. However, not all SSHv2 implementations are equal. Older Cisco implementations have known weaknesses in key exchange and encryption negotiation.
  • Cisco – The hardware and software vendor affected. This primarily targets routers, switches, and firewalls running legacy code.
  • 125 – Almost certainly refers to a RSA modulus length of 125 bytes (1000 bits) . Modern SSH standards require 2048-bit (256 bytes) or higher. A 1000-bit modulus is mathematically weak and can be factored using modern cloud computing in hours.

Thus, SSH20Cisco125 describes a vulnerability where Cisco devices, using a weak 1000-bit RSA key for SSHv2, allow an attacker to recover the private key, decrypt past sessions, or man-in-the-middle (MITM) active connections.