A flaw was found in libnbd, due to a malicious Network Block Device (NBD), a protocol for accessing Block Devices such as hard disks over a Network. This issue may allow a malicious NBD server to cause a Denial of Service.

A flaw was found in nbdcopy. When copying from NBD server using the asynchronous copy mode (default) nbdcopy may create a corrupted destination image if read or write NBD command start but the server returns an error. nbdcopy also exits with zero exit code, so programs running it cannot detect that the operation failed.

Upstream patch proposed: https://listman.redhat.com/archives/libguestfs/2022-February/msg00039.html

Structured reply is a feature of the newstyle NBD protocol allowing the server to send a reply in chunks. A bounds check which was supposed to test for chunk offsets smaller than the beginning of the request did not work because of signed/unsigned confusion. If one of these chunks contains a negative offset then data under control of the server is written to memory before the read buffer supplied by the client. If the read buffer is located on the stack then this allows the stack return address from nbdpread() to be trivially modified, allowing arbitrary code execution under the control of the server. If the buffer is located on the heap then other memory objects before the buffer can be overwritten, which again would usually lead to arbitrary code execution.