Temporal Server History Service improper authorization

Summaryinfo

A vulnerability identified as problematic has been detected in Temporal Server. The affected element is an unknown function of the component History Service. This manipulation causes improper authorization. This vulnerability is handled as CVE-2026-89140. The attack can be initiated remotely. There is not any exploit available. Applying a patch is the recommended action to fix this issue.

Detailsinfo

A vulnerability has been found in Temporal Server (affected version not known) and classified as problematic. Affected by this vulnerability is some unknown functionality of the component History Service. The manipulation with an unknown input leads to a improper authorization vulnerability. The CWE definition for the vulnerability is CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. As an impact it is known to affect integrity, and availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-89140 since 09/11/2026. The exploitation appears to be easy. The attack can be launched remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1548.002 for this issue.

Applying the patch 11876 is able to eliminate this problem.

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Productinfo

Vendor

• Temporal

Name

• Server

CPE 2.3info

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CPE 2.2info

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