CVE-2026-40196: HomeBox has Unauthorized API Access via Retained defaultGroup ID After Group Access Revocation

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-17 · updated 2026-10-26
Weakness: CWE-708

Description

HomeBox is a home inventory and organization system. Versions prior to 0.25.0 contain a vulnerability where the defaultGroup ID remained permanently assigned to a user after being invited to a group, even after their access to that group was revoked. While the web interface correctly enforced the access revocation and prevented the user from viewing or modifying the group's contents, the API did not. Because the original group ID persisted as the user's defaultGroup, and this value was not properly validated when the X-Tenant header was omitted, the user could still perform full CRUD operations on the group's collections through the API, bypassing the intended access controls. This issue has been fixed in version 0.25.0.

Affected products

sysadminsmedia homebox: before 0.25.0 — fixed in 0.25.0

How to fix

Upgrade to a fixed version: sysadminsmedia homebox 0.25.0. Check the vendor advisory for mitigations.

References

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