NetBird client: unescaped peer hostname injects OpenSSH config directives and runs commands on other peers

Impact

The NetBird client writes a system-wide OpenSSH drop-in and embeds each peer's FQDN inside a double-quoted Match host directive without escaping it. A peer name containing a double quote closes the quoted context and appends arbitrary ssh_config directives, including exec commands, which then run locally as whichever user next invokes ssh on that host. Where NetBird is the overlay that operators and automation use to reach GPU nodes, one malicious or compromised peer - or anyone who can register a peer name in the management tenant - gets code execution on every other client host, typically under the account that administers the fleet. Because the payload fires on the next ssh invocation, it rides on exactly the admin and CI sessions that hold the most privilege. Linux, macOS, Windows and FreeBSD clients are affected; the Android and iOS apps are not.

Who can reach it

A peer inside the same NetBird network, or anyone able to control a peer's registered FQDN or hostname (high privilege in the management plane). No access to the victim host is needed; execution is triggered by any local user on that host running ssh.

What to do

Upgrade NetBird clients to 0.74.7 or later, which only accepts a peer FQDN that is a valid DNS name. Rolling the client is an agent upgrade and restart per host - no node drain or reboot - but every client must be covered, since an unpatched client is the one that gets executed on. Before or after the upgrade, inspect /etc/ssh/ssh_config.d/99-netbird.conf (and the %PROGRAMDATA%\ssh equivalent) on each host for injected directives and audit peer names for quote characters.

References

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