Telepresence: Traffic Manager session hijacking via unauthenticated Tunnel endpoint (CVE-2026-102339)

The Traffic Manager Tunnel gRPC streaming endpoint in Telepresence accepts a session ID from the initial client-controlled message payload without verifying the caller's identity. This allows an attacker to supply an active session ID and receive a fully functional tunnel, gaining the network routing capabilities of the associated legitimate client. The issue is exacerbated by the lack of authentication on the ArriveAsClient endpoint, which allows attackers to generate their own valid session IDs. The vulnerability affects Telepresence versions prior to 2.31.0.

Attack Chain

1. Attacker establishes a connection to the Traffic Manager gRPC service (often exposed on port 8081).
2. Attacker invokes the ArriveAsClient endpoint to generate a session or harvests an existing session ID via log leakage.
3. Attacker initializes a Tunnel bidirectional gRPC stream.
4. Attacker sends a TunnelMessage payload containing the target victim session ID.
5. Traffic Manager processes the message in state.Tunnel and associates the attacker's stream with the victim's session in the internal map.
6. Attacker gains the ability to intercept or inject traffic into the victim's network routing context.

Impact

Successful exploitation allows an attacker to impersonate a legitimate developer session within a cluster. This grants the attacker the same network routing capabilities as the victim, enabling unauthorized access to cluster-internal resources or network paths reachable by the Telepresence client.

Recommendation

• Upgrade the Telepresence Traffic Manager to version 2.31.0 or later immediately to incorporate session ownership verification.
• Audit cluster-internal network access to the Traffic Manager gRPC service to ensure only authorized clients can reach the endpoint.
• Review centralized logging for any instances where ArriveAsClient or Tunnel endpoints are being accessed by unexpected or non-standard client service accounts.