GHSA-q939-rpr3-3284 SSH.NET: ScpClient Recursive Download Allows Arbitrary File Write via Server-Controlled SCP Filenames

• NuGet SSH.NET: < 2026.0.0 → fixed in 2026.0.0

Summary `ScpClient.Download(string directoryName, DirectoryInfo directoryInfo)` writes files and directories using names returned by the remote SCP server during recursive downloads, with no validation that the resulting path stays inside the requested local directory. A malicious, compromised, or man-in-the-middle SCP server can return names containing `../` sequences (or absolute paths), causing the client to create directories and write/overwrite files anywhere the client process has access. This is similar to OpenSSH CVE-2019-6111, but with directory traversal capability. Impact A malicious/compromised/MITM SCP server can create or write files outside the intended download directory, anywhere the client process can write. Overwriting files such as ~/.ssh/authorized_keys, shell rc files, cron entries, or application binaries/config can lead to persistence, privilege escalation, or remote code execution on the client host. Requires the victim to perform a directory download from the attacker-controlled server. Remediation The fixed release ensures that remotely-supplied file and directory names are valid local names such that the constructed local path is contained within the given local directory, and throws `ScpException` when an invalid name is detected. 600be0de543765995a189b5d7cd4efac5007f3ce