# CVE-2026-104355: Temporal Server applies inbound namespace replication from a connected peer cluster to local namespaces

> A compromised peer cluster can modify local namespace settings in Temporal Server, causing workflow failures, due to missing authorization checks on inbound replication updates.

- **Severity:** High 7.0 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 Oct 2026
- **Updated:** 16 Oct 2026
- **Also known as:** GHSA-vvgp-p2h7-g3xf

## What is CVE-2026-104355?

CVE-2026-104355 is a high-severity missing authorization vulnerability in Temporal Server, published on 12 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

A connected peer cluster can modify a Temporal Server cluster's local namespaces, which are never replicated to that peer, because the receiving cluster applies inbound namespace replication updates to them. In a multi-cluster deployment, each cluster pulls replication tasks from the remote clusters an administrator has registered with connection enabled; the sending side excludes local namespaces, but the receiving side does not apply the same rule. When an inbound task names an existing namespace, the server checks at most that the namespace identifiers match, then overwrites its state, description, owner, retention, archival settings, and cluster list, and its active cluster when the task carries a higher failover version, without checking that the namespace is global. A party that controls a registered peer's replies, by operating or compromising it, can therefore change any local namespace whose name and identifier it can supply, without any credential on the receiving cluster: for example, marking it Deprecated, making the peer its active cluster, and shortening its retention, after which new Workflow starts in that namespace fail. Local namespaces include the built-in temporal-system namespace. Namespace metadata the History service refreshes from the peer while processing its history replication tasks passes through the same logic. A cluster with no remote cluster registered with connection enabled is not exposed.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-104355?


## How do I fix CVE-2026-104355?

No fix has been published for CVE-2026-104355 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-104355 being exploited?

There is no known exploitation of CVE-2026-104355 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-104355 and fix it if it is affected.

What it is: CVE-2026-104355 is a high-severity missing authorization vulnerability in Temporal Server, published on 12 Oct 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-104355 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-2026-104355/ (Markdown: https://insights.sbomify.com/CVE-2026-104355/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-104355
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-104355
- OSV: https://osv.dev/vulnerability/CVE-2026-104355

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-104355/
Summaries are generated and may contain mistakes; the official description above is the record.