github.com/m1k1o/neko/server: Neko: Authorization bypass in legacy WebRTC input handling

Impact

When legacy mode is enabled and session.implicit_hosting is enabled, the legacy WebRTC data channel incorrectly authorizes input events due to a logic error in LegacyIsHost().

As a result, an authenticated room member may be able to send mouse and keyboard input through the legacy WebRTC control channel even when controls are locked or the member would otherwise not be authorized through the modern control API.

The issue affects only the legacy WebRTC input path. The modern HTTP/WebSocket control path correctly enforces authorization checks and is not affected.

To exploit this issue, an attacker must:

• Be authenticated as a room member.
• Successfully establish a WebRTC connection.
• Access a deployment using the legacy WebRTC input handler.

No unauthenticated access or privilege escalation outside the application is possible.

Patches

The issue has been fixed in v3.1.5 by correcting the authorization logic in the legacy WebRTC handler.

Users should upgrade to v3.1.5 or later. Fix: *395ca1a*

Workarounds

Users who cannot immediately upgrade can mitigate the issue by one of the following:

• Disable legacy mode if it is not required.
• Disable implicit hosting (session.implicit_hosting=false).
• Restrict access to trusted authenticated users.

Credits

Thanks to @KasperBuilds for responsibly disclosing this vulnerability and reaching out directly. This contribution helped strengthen the project, and the whole community benefits from it.