CVE-2026-104355 Temporal Server applies inbound namespace replication from a connected peer cluster to local namespaces
A compromised peer cluster can modify local namespace settings in Temporal Server, causing workflow failures, due to missing authorization checks on inbound replication updates.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-104355?
CVE-2026-104355 is a high-severity missing authorization vulnerability in Temporal Server, published on 12 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Official 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.
Weakness: CWE-863
Which versions are affected by CVE-2026-104355?
How do I fix CVE-2026-104355?
No fix has been published for CVE-2026-104355 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-104355 being exploited?
There is no known exploitation of CVE-2026-104355 in the wild and no public exploit code.
Sources
Also known as GHSA-vvgp-p2h7-g3xf.