Temporal Server internal completion callbacks are not bound to their namespace, allowing cross-namespace changes to Scheduler V2 schedule state
Summary
| CVE | CVE-2026-89140 |
|---|---|
| State | PUBLISHED |
| Assigner | Temporal |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-12 19:16:40 UTC |
| Updated | 2026-10-12 19:16:40 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 6 MEDIUM from [email protected]
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Problem Types: CWE-639 | CWE-639 CWE-639: Authorization Bypass Through User-Controlled Key
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 6 | MEDIUM | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C... |
| 4.0 | CNA | CVSS | 6 | MEDIUM | CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N |
CVSS v4.0 Breakdown
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Temporal Technologies Inc. | Temporal Server | affected 1.30.0 1.30.8 semver | Not specified |
| CNA | Temporal Technologies Inc. | Temporal Server | affected 1.31.0 1.31.4 semver | Not specified |
| CNA | Temporal Technologies Inc. | Temporal Server | affected 1.32.0 1.32.1 semver | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/temporalio/temporal/commit/a210eeb8c2cc7e22338bb4f552ff1171d8... | [email protected] | github.com | |
| github.com/temporalio/temporal/pull/12318 | [email protected] | github.com | |
| github.com/temporalio/temporal/releases/tag/v1.32.1 | [email protected] | github.com | |
| github.com/temporalio/temporal/pull/11876 | [email protected] | github.com | |
| github.com/temporalio/temporal/commit/d0bd72e85014f31ecfbada1b436b088064... | [email protected] | github.com | |
| github.com/temporalio/temporal/releases/tag/v1.30.8 | [email protected] | github.com | |
| github.com/temporalio/temporal/releases/tag/v1.31.4 | [email protected] | github.com | |
| github.com/temporalio/temporal/pull/12320 | [email protected] | github.com | |
| github.com/temporalio/temporal/pull/12382 | [email protected] | github.com | |
| github.com/temporalio/temporal/pull/12319 | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Reported internally at Temporal Technologies, Inc. (en)
CNA: Zellic, who independently reported this issue responsibly to Temporal Technologies (en)
CNA: V12 (en)
Additional Advisory Data
Solutions
CNA: Upgrade to Temporal Server 1.30.8, 1.31.4, or 1.32.1, as appropriate for the deployed minor release line. The fix requires no configuration change and adds no setting. When a start request attaches a temporal://internal completion callback, fixed releases decode the component reference in the callback token and reject the request with InvalidArgument unless the reference names both a namespace and a business identifier and its namespace is the namespace of the request. The check runs in the Frontend service when the callback is attached, before it is persisted; it does not apply to callbacks that were attached and persisted before the upgrade, which are delivered as before. Releases before 1.30.0 do not contain the reserved internal callback address and are not affected. On 1.32, completion callbacks attached through Workflow Update are not checked in 1.32.1. That path is off by default and is not a released feature on 1.32: keep history.enableUpdateCallbacks set to false.
Workarounds
CNA: Until a fixed release is deployed, keep Scheduler V2 schedules from being created: leave history.enableCHASMSchedulerCreation set to false, and on 1.32.0 leave history.chasmSchedulerCreationRolloutPercent at 0; do not include chasm-scheduler in frontend.allowedExperiments; and leave history.enableCHASMSchedulerMigration set to false. These settings prevent new Scheduler V2 schedules from being created; they do not remove schedules already created on Scheduler V2. Tightening component.callbacks.allowedAddresses does not help, because the reserved temporal://internal address is accepted before configured rules are evaluated. Restricting read access to the target namespace does not close the issue either, because the target namespace identifier can be visible to a caller limited to the source namespace, and it does not correct the missing authorization check.