The vulnerability exists in the ScpClient.Download method of SSH.NET versions 2025.1.0 and earlier. This method trusts file and directory names supplied by the remote SCP server and concatenates them with the local destination path without validating that the resulting path remains within the intended directory. Consequently, a malicious or compromised SSH server can provide filenames containing directory traversal sequences such as ../ or absolute paths to cause the client to create, overwrite, or delete files anywhere that the client process has write permission. This results in an arbitrary file write condition that can compromise the confidentiality, integrity, and availability of the system.

The affected product is SSH.NET, a .NET Secure Shell library, only in versions 2025.1.0 and earlier. The vulnerability is fixed in release 2026.0.0.

The overall CVSS score of 7.1 indicates a moderate to high impact severity. The EPSS score is not available, so the current likelihood of exploitation is unknown at this time, but the vulnerability is listed as not in the CISA KEV catalog. The attack vector is remote and relies on a malicious or man‑in‑the‑middle SSH server that the client trusts. An attacker controlling such a server can initiate a recursive download that writes arbitrary files on the client, assuming the client process has sufficient local permissions. The absence of containment checks means the threat is executable without additional privileges, making it a realistic risk for any application that performs SCP downloads with SSH.NET.