SeaweedFS: Filer JWT allowed_prefixes literal prefix match allows cross-tenant access to sibling paths (CVE-2026-72921)

The vulnerability in SeaweedFS (CVE-2026-72921) affects the filer JWT authorization mechanism where the allowed_prefixes check uses a literal string prefix match (strings.HasPrefix). This causes tokens scoped to a prefix such as /tenant1 to also authorize access to sibling paths with similar prefixes (e.g., /tenant1234), resulting in cross-tenant authorization bypass. Both read and write operations are affected. The flaw is in the filer_server_handlers.go component. The fix, introduced in version 4.24, changes the check to match on /-separated path components after path.Clean normalization, restricting tokens to their exact prefix and descendants only.

An attacker with a valid JWT token scoped to one tenant can access data belonging to other tenants by exploiting the prefix matching flaw. This leads to unauthorized cross-tenant read and write access, compromising data confidentiality and integrity within multi-tenant SeaweedFS deployments. The vulnerability requires a valid scoped token, so it is an authorization bypass rather than unauthenticated access.

A patch is available in SeaweedFS version 4.24 that fixes the authorization check to correctly match path components. Users should upgrade to version 4.24 or later. As a workaround, where feasible, tenants should choose prefix names that are not string-prefixes of one another, for example by using a trailing separator convention to avoid ambiguous prefix matches.