SSH0: Exchanging versions - SSH-2.0-Cisco-1.25 SSH0: send SSH message: outdated is NULL server version string:SSH-2.0-Cisco-1.25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 server has also demonstrated fragility with key exchange algorithms. A specific bug reported to Cisco (BugID CSCvr33381) describes a scenario where, in about 10% of incoming SSH connections to an IOS-XE router, the SSH server fails to respond to the client's SSH2_MSG_KEXINIT key exchange message. This effectively "stalls" the SSH handshake, preventing any connection from being established and causing a localized but unpredictable denial of service for administrative access.

Monitored via Cisco Bug ID CSCwi61646 , the actively degrades connection security.

Log into the device and run:

While the SSH-2.0-Cisco-1.25 string is often associated with legacy code, the risk is not confined to the past. Cisco has disclosed several high-severity vulnerabilities in recent years that affect modern products and their SSH implementations.

Limit SSH access to specific management subnets to reduce the attack surface.

If you see this banner, the device is likely vulnerable to one or more of the following:

Academic and industry scans have consistently detected the SSH-2.0-Cisco-1.25 banner in significant numbers globally. The real-world viability of these vulnerabilities is supported by the fact that some of the associated CVEs (particularly CVE-2015-0721) have exploit modules available in frameworks like , showing that exploitation is not just theoretical.

When an SSH client connects to an SSH server, the server identifies itself with a version string. The standard format is: SSH-protocol version-software version comments .

: This has been observed in environments reporting the SSH-2.0-Cisco-1.25 banner. 3. Weak Cryptographic Algorithms

: The software suffers from an architectural state handling defect during the initial cryptographic handshake before user credentials are validated. An attacker can intentionally structure protocol messages out of order.