In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: dummy: fix UMP event stack overread

The dummy sequencer port forwards events by copying an incoming struct sndseqevent into a stack temporary, rewriting source and destination, and dispatching the temporary to subscribers. That legacy event storage is smaller than struct sndsequmpevent.

When a UMP event reaches the dummy client, the copy leaves the UMP flag set but only provides legacy-sized stack storage. The subscriber delivery path then uses sndseqeventpacketsize() and copies a UMP-sized packet from that stack object, reading past the end of the temporary.

Use the existing union sndseqevent storage and copy the packet size reported for the incoming event before rewriting the common routing fields. This preserves the full UMP packet for UMP events while keeping legacy event handling unchanged.