# CVE-2026-89140: Missing authorization in Temporal Server

> Authenticated users can modify Scheduler V2 state in other namespaces by forging internal completion callbacks, bypassing namespace isolation.

- **Severity:** Medium 6.0 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Oct 2026
- **Updated:** 16 Oct 2026
- **Also known as:** GHSA-fmmr-q3xv-r2hc

## What is CVE-2026-89140?

CVE-2026-89140 is a medium-severity missing authorization vulnerability in Temporal Server, published on 12 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official 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.

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-89140?


## How do I fix CVE-2026-89140?

No fix has been published for CVE-2026-89140 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-89140 being exploited?

There is no known exploitation of CVE-2026-89140 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89140 and fix it if it is affected.

What it is: CVE-2026-89140 is a medium-severity missing authorization vulnerability in Temporal Server, published on 12 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-89140 in the wild and no public exploit code.

Affected product: Temporal Server. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-89140/ (Markdown: https://insights.sbomify.com/CVE-2026-89140/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89140
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89140
- OSV: https://osv.dev/vulnerability/CVE-2026-89140

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89140/
Summaries are generated and may contain mistakes; the official description above is the record.