# CVE-2026-82431: Apache Storm Client: Authorization Bypass When nimbus.groups Is Configured Without nimbus.users

> Authenticated users can perform restricted operations if group-based access control is configured without user lists, bypassing intended security restrictions.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Sep 2026
- **Updated:** 14 Sep 2026
- **Also known as:** GHSA-45m3-3j6g-xv67

## What is CVE-2026-82431?

CVE-2026-82431 is a critical missing authorization vulnerability in Apache Storm Client, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Description

`SimpleACLAuthorizer` evaluated the user-level command set by returning early when `nimbus.users` was empty,
before `nimbus.groups` was considered. An operator who restricted cluster access by group alone, leaving
`nimbus.users` unset, therefore received no restriction at all: every authenticated principal was permitted
every user-level operation, including `submitTopology`, `beginFileUpload` and `getNimbusConf`.

`docs/SECURITY.md` presents `nimbus.groups` as a supported way to lock down a cluster, so a deployment
following the documentation could believe it was restricted while it was not. The failure is silent; nothing
in the logs or the configuration indicates that the group list is being ignored.

Both lists left empty continues to mean that no restriction is configured, which is the shipped default and
is unchanged.

Mitigation

Upgrade to 3.1.0, where `nimbus.groups` is evaluated whether or not `nimbus.users` is set.

Users who cannot upgrade immediately should additionally populate `nimbus.users` with the intended
principals, since a non-empty user list causes the group list to be evaluated on affected versions.
Operators should review Nimbus access logs for operations by principals outside the intended groups.

Note that after upgrading, a cluster configured with `nimbus.groups` alone becomes restrictive for the first
time. This includes `NimbusClient`, which calls `getLeader` on every connection, so clients outside the
configured groups will begin to be refused.

Credit

The ASF -- found using Claude agents to study the security of open-source projects, validated and reported by Apache Storm.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-82431?


## How do I fix CVE-2026-82431?

No fix has been published for CVE-2026-82431 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-82431 being exploited?

There is no known exploitation of CVE-2026-82431 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-82431 and fix it if it is affected.

What it is: CVE-2026-82431 is a critical missing authorization vulnerability in Apache Storm Client, published on 14 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-82431 in the wild and no public exploit code.

Affected product: Apache Storm Client. 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-2026-82431/ (Markdown: https://insights.sbomify.com/CVE-2026-82431/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-82431
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-82431
- OSV: https://osv.dev/vulnerability/CVE-2026-82431

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-82431/
Summaries are generated and may contain mistakes; the official description above is the record.