CVE-2026-85756

SSH.NET: ScpClient allows server-side RCE via default SCP path handling

Default SCP remote-path handling places caller-supplied paths into the command that runs scp on the server. On a shell-based server that command is interpreted by a shell, so an attacker-influenced path that is not quoted to suit that shell can execute as a command as the authenticated SSH user. SSH.NET provides ScpClient.RemotePathTransformation to control escaping behaviour (defaulting to RemotePathTransformation.DoubleQuote) but cannot guarantee safety for arbitrary remote command interpreters. This is inherent to running scp over a remote shell (cf. CVE-2020-15778).

Command execution on the SSH server as the authenticated SSH user, when an application passes an attacker-influenced remote path to ScpClient against a shell-based server.

Exploitation depends on conditions beyond the attacker's control: the remote server must be shell-based, and the attacker-influenced path must be crafted to defeat the quoting applied by the transformation in effect, that is, to use metacharacters that it does not neutralise (for example $(...) or backticks, which survive the default double-quoting on a POSIX shell). A path that does not meet these escaping rules, or a non-shell-based server, does not result in command execution.

Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.

CVE-2026-85756 has a CVSS score of 7.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2026.0.0); upgrading removes the vulnerable code path.

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The fixed release obsoletes the constructors that silently defaulted the path transformation and adds constructors that require an explicit IRemotePathTransformation, so callers are required to choose one that suits their server and trust environment. For POSIX shells, the library provides RemotePathTransformation.ShellQuote. The legacy default (RemotePathTransformation.DoubleQuote) is unchanged for backwards compatibility. SCP is considered legacy and SFTP, which does not involve a remote shell, is recommended where possible (via SftpClient).

1. What is CVE-2026-85756? CVE-2026-85756 is a high-severity OS command injection vulnerability in SSH.NET (nuget), affecting versions < 2026.0.0. It is fixed in 2026.0.0. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
2. How severe is CVE-2026-85756? CVE-2026-85756 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of SSH.NET are affected by CVE-2026-85756? SSH.NET (nuget) versions < 2026.0.0 is affected.
4. Is there a fix for CVE-2026-85756? Yes. CVE-2026-85756 is fixed in 2026.0.0. Upgrade to this version or later.
5. Is CVE-2026-85756 exploitable, and should I be worried? Whether CVE-2026-85756 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-85756 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-85756? Upgrade SSH.NET to 2026.0.0 or later.