CVE-2026-55678 Arc: Unauthenticated cluster node admission when `cluster.shared_secret` is unset
Unauthenticated attackers can join Arc Enterprise clusters if shared_secret is unset, allowing them to intercept data, modify cluster state, and execute operations as trusted nodes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-55678?
CVE-2026-55678 is a medium-severity missing authorization vulnerability in Basekick-Labs arc, published on 28 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-55678?
3 open source packages ship an affected version, including github.com/basekick-labs/arc.
| Package | Affected | Fixed in |
|---|---|---|
github.com/basekick-labs/arc Go | All versions | 0.0.0-20260615160325-38402ad2ebdd |
github.com/basekick-labs/arc Go | All versions | 0.0.0-20260615160325-38402ad2ebdd |
github.com/basekick-labs/arc Go | All versions | 0.0.0-20260615160325-38402ad2ebdd |
How do I fix CVE-2026-55678?
Upgrade github.com/basekick-labs/arc to 0.0.0-20260615160325-38402ad2ebdd or later.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-55678 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55678 exists.
Sources
Also known as GHSA-p378-jp5r-gpgw, GO-2026-6322.