CVE-2026-89140 Temporal Technologies, Inc. CVE debrief

Who should care

Defenders responsible for Temporal Server deployments, specifically those using Scheduler V2, should assess exposure and prioritize verification and remediation. They should review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance. Defenders should also plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Why it matters

CVE-2026-89140 is a medium-severity vulnerability in Temporal Server that allows an authenticated caller to alter Scheduler V2 schedule state in another namespace. Defenders should prioritize verification, remediation, and monitoring to prevent potential exploitation and unintended consequences.

• Defenders must verify and upgrade to patched versions to prevent exploitation
• Scheduler V2 configuration and monitoring must be reviewed to detect potential suspicious activity
• Cross-namespace changes to schedule state could lead to unintended consequences

Technical summary

Temporal Server does not bind internal completion callbacks to the namespace that attached them, allowing an authenticated caller with write permission in one namespace to alter Scheduler V2 schedule state in another namespace. This vulnerability can be exploited by an attacker with write permission in one namespace to alter Scheduler V2 schedule state in another namespace, potentially leading to unintended consequences. The callback address temporal://internal is reserved for callbacks that Scheduler V2 attaches to the Workflows it starts.

Defensive priority

Defenders should prioritize verifying and upgrading to patched versions of Temporal Server, specifically versions 1.30.8, 1.31.4, or 1.32.1, and ensure that Scheduler V2 is properly configured.

Recommended defensive actions

• Verify and upgrade to patched versions of Temporal Server
• Ensure Scheduler V2 is properly configured
• Monitor for suspicious activity
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and source item provide details on the vulnerability, including its description, affected versions, and references to patches and fixes. The Temporal Server internal completion callbacks are not bound to their namespace, allowing cross-namespace changes to Scheduler V2 schedule state. This vulnerability requires the target namespace identifier, the schedule identifier, and the identity and timing of the callback.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.