CVE-2019-14842

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
nbd_pread() 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.

Bugs

• <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=942215&gt;