Description
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.
Published: 2026-10-12
Score: 7 High
EPSS: < 1% Very Low
KEV: No
Impact: Unauthorized Namespace Modification
Action: Immediate Patch
AI Analysis

Impact

A connected peer cluster can apply inbound namespace replication tasks that overwrite the metadata of local namespaces in the receiving cluster, without requiring any authentication on the target cluster. The flaw allows an attacker to change the name, description, owner, retention policy, archival settings, cluster list, and active cluster for any local namespace that matches a supplied identifier. This capability can render workflows in the affected namespace unattainable, reduce data retention, or compromise system integrity.

Affected Systems

Temporal Technologies, Inc. Temporal Server is affected in all releases prior to 1.30.8, covering the 1.30, 1.31, and 1.32 supported lines. Fixed releases are 1.30.8, 1.31.4, and 1.32.1; operators using 1.29.7 and earlier are outside the supported window and must upgrade to a supported line.

Risk and Exploitability

The CVSS score of 7 indicates a moderate‑to‑high severity. EPSS information is not available, and the vulnerability is not listed in the CISA KEV catalog. The likely attack vector is inferred from the description: an attacker who controls or compromises a registered remote cluster can inject malicious replication tasks to modify local namespaces by supplying matching identifiers, without needing any credentials on the receiving cluster. The threat is significant for any multi‑cluster deployment where trust boundaries are not strictly enforced.

Generated by OpenCVE AI on October 12, 2026 at 21:36 UTC.

Remediation

Vendor Solution

Upgrade to Temporal Server 1.30.8, 1.31.4, or 1.32.1, as appropriate for the deployed minor release line, and keep the dynamic configuration setting history.validateReplicationTaskSourceCluster at its default of true. Fixed releases ignore an inbound namespace replication task, including one applied through the namespace metadata refresh that history replication can trigger, when it targets a namespace the receiving cluster stores as local, and ignore inbound task queue user data replication for a local namespace. With history.validateReplicationTaskSourceCluster enabled, fixed releases also ignore an inbound history replication task when the sending cluster is not in the namespace's cluster list, which for a local namespace is every remote cluster. The fix does not change how a connected peer can update a global namespace replicated with the receiving cluster. Fixed releases do not repair a local namespace that was already modified; review local namespaces, including temporal-system, as described in the workarounds. Temporal Server releases up to and including 1.29.7 are outside the supported window and receive no fix; operators on those releases should upgrade to a supported line.

Vendor Workaround

Until upgrading, register a remote cluster, and keep its connection enabled, only when that cluster and everyone able to control it are trusted with administrative authority over every namespace on the receiving cluster, including its local namespaces and temporal-system. Disabling the connection to a remote cluster stops the receiving cluster from pulling replication tasks from it, and also stops legitimate replication of global namespaces with that cluster. Review local namespaces, including temporal-system, for a cluster list or active cluster other than the current cluster.

OpenCVE Recommended Actions

  • Upgrade to a fixed release (1.30.8, 1.31.4, or 1.32.1) and keep the dynamic configuration setting history.validateReplicationTaskSourceCluster at its default of true.
  • If immediate upgrade is not possible, register a remote cluster only when that cluster and all its administrators have full administrative authority over all namespaces, including local namespaces and temporal-system, and keep the connection enabled; otherwise disable the connection to that cluster so the receiving cluster does not pull replication tasks.
  • After upgrading or reconfiguring, review all local namespaces (including temporal-system) for incorrect cluster lists or active cluster settings and correct any that allow the cluster to appear as a valid target.

Generated by OpenCVE AI on October 12, 2026 at 21:36 UTC.

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History

Tue, 10 Nov 2026 21:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Mon, 12 Oct 2026 19:00:00 +0000

Type Values Removed Values Added
Description 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.
Title Temporal Server applies inbound namespace replication from a connected peer cluster to local namespaces
First Time appeared Temporal
Temporal temporal
Weaknesses CWE-863
CPEs cpe:2.3:a:temporal:temporal:*:*:*:*:*:*:*:*
Vendors & Products Temporal
Temporal temporal
References
Metrics cvssV4_0

{'score': 7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N'}

Subscriptions

Temporal Temporal
cve-icon MITRE

Status: PUBLISHED

Assigner: Temporal

Published:

Updated: 2026-10-16T17:50:59.464Z

Reserved: 2026-10-01T20:45:19.047Z

Link: CVE-2026-104355

cve-icon Vulnrichment

Updated: 2026-10-16T17:50:56.041Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-12T19:16:36.900

Modified: 2026-10-16T19:55:59.740

Link: CVE-2026-104355

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-10-12T22:00:16Z

Weaknesses