CVE-2026-82431

/// Technical 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 addi

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References