Bug 2549872 (CVE-2026-104355)

Summary: CVE-2026-104355 go.temporal.io/server: Temporal Server: Unauthorized modification of local namespaces via inbound replication tasks
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: blitton, mbarnett
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Temporal Server. In a multi-cluster deployment, the server fails to verify whether inbound replication tasks apply only to global namespaces. An attacker controlling a connected peer cluster can exploit this vulnerability by sending replication updates that overwrite configuration settings for local namespaces. This unauthorized modification can alter namespace states and disrupt operations, leading to a Denial of Service (DoS) for workflows running in affected namespaces.
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Description OSIDB Bzimport 2026-10-12 19:02:27 UTC 
A connected peer cluster can modify a Temporal Server cluster's local namespaces, which are never replicated to that peer, because the receiving cluster applies inbound namespace replication updates to them. In a multi-cluster deployment, each cluster pulls replication tasks from the remote clusters an administrator has registered with connection enabled; the sending side excludes local namespaces, but the receiving side does not apply the same rule. When an inbound task names an existing namespace, the server checks at most that the namespace identifiers match, then overwrites its state, description, owner, retention, archival settings, and cluster list, and its active cluster when the task carries a higher failover version, without checking that the namespace is global. A party that controls a registered peer's replies, by operating or compromising it, can therefore change any local namespace whose name and identifier it can supply, without any credential on the receiving cluster: for example, marking it Deprecated, making the peer its active cluster, and shortening its retention, after which new Workflow starts in that namespace fail. Local namespaces include the built-in temporal-system namespace. Namespace metadata the History service refreshes from the peer while processing its history replication tasks passes through the same logic. A cluster with no remote cluster registered with connection enabled is not exposed.