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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
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.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-82431 being exploited?
There is no known exploitation of CVE-2026-82431 in the wild and no public exploit code.
Sources
Also known as GHSA-45m3-3j6g-xv67.