CVE-2026-55678: basekick-labs arc Improper Access Control

Vulnerability summary

CVE-2026-55678 is a medium (CVSS 6.9) Improper Access Control vulnerability in basekick-labs arc. EPSS estimates a 0.66% chance of exploitation in the next 30 days, higher than 51.1% of scored vulnerabilities.

Timeline

1. 28-08-2026
   PublishedVulnerability first disclosed.
2. 01-09-2026
   Last modifiedVulnerability information updated.

Description

Arc is an open, SQL-native time-series database for telemetry. From 26.02.1 until 26.06.2, Arc Enterprise clustering accepts cluster join requests without authentication when cluster.enabled is true but cluster.shared_secret is not configured. The defaults in internal/config/config.go set cluster.enabled to false, cluster.cluster_name to arc-cluster, cluster.coordinator_addr to :9100, cluster.shared_secret to an empty value, and cluster.tls_enabled to false, while cmd/arc/main.go requires cluster.shared_secret only when cluster.replication_enabled is true. JoinRequest in internal/cluster/protocol/messages.go accepts attacker-controlled node_id, role, raft_addr, api_addr, and coord_addr values, plus optional auth_nonce, auth_timestamp, and auth_hmac fields. The join path in internal/cluster/coordinator.go validates HMAC authentication only when the configured shared secret is non-empty and otherwise proceeds after only the cluster-name check. An accepted node is marked healthy, added as a Raft voter or registered locally, and becomes available through internal/cluster/registry.go to the routing logic in internal/cluster/router.go. The forwardRequest path in internal/cluster/router.go builds its target from node.APIAddress and copies Authorization and x-api-key headers with the request, so a rogue node selected for a forwarded query or write can receive authentication headers, request bodies, database and measurement names, and operational metadata. Heartbeat in internal/cluster/protocol/messages.go also lacks HMAC fields, and internal/cluster/coordinator.go updates node state from supplied node_id and state values without authentication. An unauthenticated network attacker who can reach the coordinator port and knows the cluster name can therefore become a trusted cluster node, mutate cluster membership, be submitted as a Raft voter, intercept topology-dependent forwarded requests, divert or forge operations, and blackhole or delay traffic. The default standalone configuration is not reachable because cluster.enabled is false, but Enterprise cluster deployments with clustering enabled and no shared secret are affected. This issue is fixed in version 26.06.2.

• CWE-284Improper Access ControlThe product does not restrict or incorrectly restricts access to a resource from an unauthorized actor.
• CWE-287Improper AuthenticationWhen an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
• CWE-306Missing Authentication for Critical FunctionThe product does not perform any authentication for functionality that requires a provable user identity or consumes a significant amount of resources.