Security audits often list this as a "medium" or "low" risk because of Information Disclosure
However, the prevalence of this banner is significant because it signals the potential presence of various historical and modern critical vulnerabilities, including unpatched CVE-2002-1359 , the CVE-2015-0721 AAA bypass, and recent high-severity CVEs like CVE-2024-20526 . This article will dissect the technical nature of the SSH banner, analyze the critical vulnerabilities historically and currently associated with the device families that display it, and provide comprehensive mitigation strategies.
: 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)
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. ssh-2.0-cisco-1.25 vulnerability
If the device was previously using weak keys, generate new, stronger keys.
: Leverage Nessus, OpenVAS, or similar scanners. Plugins like 165676 can actively test for known Cisco vulnerabilities by attempting to authenticate and send specific SSH requests to identify vulnerable versions.
When security scanners report a flaw against an SSH-2.0-Cisco-1.25 banner, they are generally checking for one of several prominent Cisco Security Advisories. 1. Authentication Bypass Vulnerabilities (RSA Key Flaws) Security audits often list this as a "medium"
SSH0: Exchanging versions - SSH-2.0-Cisco-1.25 SSH0: send SSH message: outdated is NULL server version string:SSH-2.0-Cisco-1.25
The SSH-2.0-Cisco-1.25 banner is a relic of a previous era of network management. Seeing this banner on a network device today should be considered a significant operational risk indicator. It almost always points to an older system with potential interoperability issues, weak cryptographic defaults, and a susceptibility to a wide range of unpatched vulnerabilities, including those that enable denial of service, remote command execution, and bypass of security controls.
The identification string SSH-2.0-Cisco-1.25 is a common sight for network engineers, appearing during SSH connections to a vast number of Cisco switches and routers. It is not merely a version number; it's a digital banner announced by the SSH server on a device as soon as a TCP connection is established on port 22. Erlang SSH Remote Code Execution (RCE) SSH-2
This string indicates that the device is running a specific, often older or unpatched, version of the Cisco SSH server implementation. While appearing as "SSH-2.0", which suggests the standard Secure Shell Protocol version 2, the implementation details within 1.25 often correspond to older Cisco IOS or Cisco IOS-XE releases. Why is it Flagged as a Vulnerability?
! Example Configuration Hardening ip ssh server algorithm encryption aes128-ctr aes192-ctr aes256-ctr ip ssh server algorithm mac hmac-sha2-256 hmac-sha2-512 ip ssh server algorithm kex diffie-hellman-group14-sha256 Use code with caution. 4. Implement Strict Access Control
ip access-list standard MGMT_HOSTS permit 10.100.50.0 0.0.0.255 ! line vty 0 4 access-class MGMT_HOSTS in transport input ssh Use code with caution. Step 3: Hardening Cryptographic Ciphers