CVE-2026-89140 Missing authorization in Temporal Server
Authenticated users can modify Scheduler V2 state in other namespaces by forging internal completion callbacks, bypassing namespace isolation.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-89140?
CVE-2026-89140 is a medium-severity missing authorization vulnerability in Temporal Server, published on 12 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
Temporal Server does not bind internal completion callbacks to the namespace that attached them, which allows an authenticated caller with write permission in one namespace to alter Scheduler V2 schedule state in another namespace. The callback address temporal://internal is reserved for callbacks that Scheduler V2 attaches to the Workflows it starts. In affected releases, any authenticated caller could attach a callback with that address to a Workflow start request, the address was exempt from the component.callbacks.allowedAddresses allowlist, and the History service delivered the callback to the component its token named, in whatever namespace that was, without authorizing the original caller there. When the forged completion matches an action a target schedule is running, the schedule records the action as completed while its Workflow still runs, which can defeat an overlap policy such as SKIP, and passes caller-controlled data to the next scheduled Workflow as its last completion result. A forged failure may also pause a schedule configured to pause on failure. A forgery requires the target namespace identifier, the schedule identifier, and the identity and timing of a running action. No disclosure of Workflow payloads or history was identified. Only namespaces that hold Scheduler V2 schedules can be targeted; Scheduler V2 is off by default, and existing Scheduler V2 schedules remain targets after the settings that create them are turned off.
Weakness: CWE-639
Which versions are affected by CVE-2026-89140?
How do I fix CVE-2026-89140?
No fix has been published for CVE-2026-89140 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-2026-89140 being exploited?
There is no known exploitation of CVE-2026-89140 in the wild and no public exploit code.
Sources
Also known as GHSA-fmmr-q3xv-r2hc.