Exploitation requires all of the following. Authorization must be enabled through a configured authorizer and claim mapper; without it every caller already holds write permission in every namespace and there is no boundary to cross. The caller must be able to start a Workflow with completion callbacks in some namespace. The target namespace must hold a Scheduler V2 schedule. On 1.30.x that requires history.enableChasm, which defaults to false on that line, together with a Scheduler V2 creation route. On 1.31.x and 1.32.0, where the CHASM engine is enabled by default, it requires a Scheduler V2 creation route alone. The creation routes are history.enableCHASMSchedulerCreation, which defaults to false, gated on 1.32.0 by history.chasmSchedulerCreationRolloutPercent, which defaults to 0; the chasm-scheduler entry in frontend.allowedExperiments, which is empty by default; and history.enableCHASMSchedulerMigration, which defaults to false. Scheduler V2 is a first-party feature, and a deployment that enables it is in scope.
"}],"value":"Exploitation requires all of the following. Authorization must be enabled through a configured authorizer and claim mapper; without it every caller already holds write permission in every namespace and there is no boundary to cross. The caller must be able to start a Workflow with completion callbacks in some namespace. The target namespace must hold a Scheduler V2 schedule. On 1.30.x that requires history.enableChasm, which defaults to false on that line, together with a Scheduler V2 creation route. On 1.31.x and 1.32.0, where the CHASM engine is enabled by default, it requires a Scheduler V2 creation route alone. The creation routes are history.enableCHASMSchedulerCreation, which defaults to false, gated on 1.32.0 by history.chasmSchedulerCreationRolloutPercent, which defaults to 0; the chasm-scheduler entry in frontend.allowedExperiments, which is empty by default; and history.enableCHASMSchedulerMigration, which defaults to false. Scheduler V2 is a first-party feature, and a deployment that enables it is in scope."},{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"The Attack Requirements metric is Present because a forged completion changes schedule state only when it matches an action the target schedule is running at the time of delivery, and a nonmatching completion is accepted without effect. Exploitation under a known schedule identifier and interval has been demonstrated; exploitation without synchronized timing has not. The Base score reflects the demonstrated integrity effect and does not score the forged-failure availability effect, which has not been reproduced.
"}],"value":"The Attack Requirements metric is Present because a forged completion changes schedule state only when it matches an action the target schedule is running at the time of delivery, and a nonmatching completion is accepted without effect. Exploitation under a known schedule identifier and interval has been demonstrated; exploitation without synchronized timing has not. The Base score reflects the demonstrated integrity effect and does not score the forged-failure availability effect, which has not been reproduced."}],"credits":[{"lang":"en","type":"finder","value":"Reported internally at Temporal Technologies, Inc."},{"lang":"en","type":"finder","value":"Zellic, who independently reported this issue responsibly to Temporal Technologies"},{"lang":"en","type":"tool","value":"V12"}],"descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"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.
"}],"value":"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."}],"impacts":[{"descriptions":[{"lang":"en","value":"Unauthorized modification of Scheduler V2 schedule state in a namespace where the caller holds no permission. Confirmed effects are recording a still-running scheduled Workflow as completed, removing it from the schedule's running actions, and supplying caller-controlled data to the next scheduled Workflow as its last completion result. A forged failure can pause a schedule configured to pause on failure; that effect is supported by source review but has not been reproduced. No disclosure of Workflow payloads or history, code execution, or Temporal Server process crash was identified."}]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":6,"baseSeverity":"MEDIUM","exploitMaturity":"NOT_DEFINED","privilegesRequired":"LOW","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-639","description":"CWE-639: Authorization Bypass Through User-Controlled Key","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-10-12T18:44:23.032Z","orgId":"61241ed8-fa44-4f23-92db-b8c443751968","shortName":"Temporal"},"references":[{"name":"Fix pull request","tags":["patch"],"url":"https://github.com/temporalio/temporal/pull/11876"},{"name":"Fix commit","tags":["patch"],"url":"https://github.com/temporalio/temporal/commit/a210eeb8c2cc7e22338bb4f552ff1171d8f35969"},{"name":"Backport pull request for the 1.30 release line","tags":["patch"],"url":"https://github.com/temporalio/temporal/pull/12318"},{"name":"Backport pull request for the 1.31 release line","tags":["patch"],"url":"https://github.com/temporalio/temporal/pull/12319"},{"name":"Follow-up pull request for the 1.31 release line, checking every reading of the callback token","tags":["patch"],"url":"https://github.com/temporalio/temporal/pull/12382"},{"name":"Backport pull request for the 1.32 release line","tags":["patch"],"url":"https://github.com/temporalio/temporal/pull/12320"},{"name":"Backport commit on release/v1.32.x","tags":["patch"],"url":"https://github.com/temporalio/temporal/commit/d0bd72e85014f31ecfbada1b436b08806496dbef"},{"name":"Temporal Server 1.30.8","tags":["release-notes"],"url":"https://github.com/temporalio/temporal/releases/tag/v1.30.8"},{"name":"Temporal Server 1.31.4","tags":["release-notes"],"url":"https://github.com/temporalio/temporal/releases/tag/v1.31.4"},{"name":"Temporal Server 1.32.1","tags":["release-notes"],"url":"https://github.com/temporalio/temporal/releases/tag/v1.32.1"}],"solutions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"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.
"}],"value":"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."}],"source":{"discovery":"INTERNAL"},"title":"Temporal Server internal completion callbacks are not bound to their namespace, allowing cross-namespace changes to Scheduler V2 schedule state","workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"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.
"}],"value":"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."}]}},"cveMetadata":{"assignerOrgId":"61241ed8-fa44-4f23-92db-b8c443751968","assignerShortName":"Temporal","cveId":"CVE-2026-89140","datePublished":"2026-10-12T18:44:23.032Z","dateReserved":"2026-09-10T23:08:28.591Z","dateUpdated":"2026-10-12T18:44:23.032Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-10-12 19:16:40","lastModifiedDate":"2026-10-12 19:16:40","problem_types":["CWE-639","CWE-639 CWE-639: Authorization Bypass Through User-Controlled Key"],"metrics":{"cvssMetricV40":[{"source":"security@temporal.io","type":"Secondary","cvssData":{"version":"4.0","vectorString":"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","baseScore":6,"baseSeverity":"MEDIUM","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"LOW","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"89140","Ordinal":"1","Title":"Temporal Server internal completion callbacks are not bound to t","CVE":"CVE-2026-89140","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"89140","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Temporal Server internal completion callbacks are not bound to t"}]}}}