CVE-2025-47711: Nbdkit: nbdkit-server: off-by-one error when processing block status may lead to a denial of service

The nbdkit server had an off-by-one error when processing block status results from plugins on behalf of an NBD client. If a client requests block status for the maximum 32-bit length, and the plugin reports a larger length as a single extent, then nbdkit hits an assertion failure. A compliant client could use this to cause a denial-of-service attack against the server to prevent it from serving other clients.

— Red Hat

There's a flaw in the nbdkit server when handling responses from its plugins regarding the status of data blocks. If a client makes a specific request for a very large data range, and a plugin responds with an even larger single block, the nbdkit server can encounter a critical internal error, leading to a denial-of-service.

— MITRE