MediumCVE-2026-89140

    Temporal Server: Authorization Bypass Through User-Controlled Key (CVE-2026-89140)

    Published Last modified Sources: CVE.org

    What is affected, what to do

    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.

    Update Temporal Server to version 1.30.8, Temporal Server to version 1.31.4, Temporal Server to version 1.32.1.

    Affected
    • Temporal Server lt 1.30.0..1.30.8
    • Temporal Server lt 1.31.0..1.31.4
    • Temporal Server lt 1.32.0..1.32.1
    Fixed in
    • Temporal Server 1.30.8
    • Temporal Server 1.31.4
    • Temporal Server 1.32.1

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    6.0

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v4

    6.0

    CVSS v4

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org

    0.3 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 26.1

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    65.47 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    6.0 Methodology
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.0
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.3 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    26.1
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 16 October 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-639

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    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.

    Source: cvelistv5, NVD (NIST)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    Temporal Technologies, Inc.Temporal Server
    • 1.30.0 – < 1.30.8
    • 1.32.0 – < 1.32.1
    • 1.31.0 – < 1.31.4
    • 1.30.8
    • 1.32.1
    • 1.31.4

    Vendors and products

    Weakness classes (CWE)

    • CWE-639Authorization Bypass Through User-Controlled Key

      Base

      The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.

      Entry at MITRE CWE-639

    References & sources

    • github.comFix pull requestPatch
    • github.comFix commitPatch
    • github.comBackport pull request for the 1.30 release linePatch
    • github.comBackport pull request for the 1.31 release linePatch
    • github.comFollow-up pull request for the 1.31 release line, checking every reading of the callback tokenPatch
    • github.comBackport pull request for the 1.32 release linePatch
    • github.comBackport commit on release/v1.32.xPatch
    • github.comTemporal Server 1.30.8Release notes
    • github.comTemporal Server 1.31.4Release notes
    • github.comTemporal Server 1.32.1Release notes

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-89140","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-16T17:51:46.683270Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. Receivedtemporal.io

      CVSS V4.0: AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

      Weakness type: CWE-639

      Description added or changed

      Show 14 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      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.
      CVSSadded
      —
      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
      Weakness type (CWE)added
      —
      CWE-639
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/89xxx/CVE-2026-89140.json">CVE-2026-89140</a>
      Referenceadded
      —
      https://github.com/temporalio/temporal/commit/a210eeb8c2cc7e22338bb4f552ff1171d8f35969
      Referenceadded
      —
      https://github.com/temporalio/temporal/commit/d0bd72e85014f31ecfbada1b436b08806496dbef
      Referenceadded
      —
      https://github.com/temporalio/temporal/pull/11876
      Referenceadded
      —
      https://github.com/temporalio/temporal/pull/12318
      Referenceadded
      —
      https://github.com/temporalio/temporal/pull/12319
      Referenceadded
      —
      https://github.com/temporalio/temporal/pull/12320
      Referenceadded
      —
      https://github.com/temporalio/temporal/pull/12382
      Referenceadded
      —
      https://github.com/temporalio/temporal/releases/tag/v1.30.8
      Referenceadded
      —
      https://github.com/temporalio/temporal/releases/tag/v1.31.4
      Referenceadded
      —
      https://github.com/temporalio/temporal/releases/tag/v1.32.1

      Source identifier: security@temporal.io

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