CVE-2026-89479

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

sctp: stop processing a packet once its association is deleted

sctp endpoint bh rcv() looks the association up only when chunk->asoc is NULL, and caches the result in chunk->asoc and chunk->transport without taking a reference.

A packet that matches no association is handed to the endpoint, so a peer can bundle COOKIE ECHO, SHUTDOWN and SHUTDOWN ACK in one packet. The COOKIE ECHO creates the association, the SHUTDOWN chunk caches it, and with the outqueue empty the SHUTDOWN ACK reaches sctp sf do 9 2 final(), so the association and its transports are freed.

The endpoint loop has no counterpart to the asoc->base.dead check in sctp assoc bh rcv(). The next chunk writes to last time heard in the freed transport and is then passed to sctp do sm() with the freed association. The transport is freed through RCU, so this needs the packet to come off the socket backlog, where the loop runs in task context.

The endpoint loop cannot do the same check: it holds no reference on the association, so reading asoc->base.dead would itself be a use-after-free. Mark the packet for discard in the command interpreter, just before it deletes the association. That is also before sctp inq free() releases the chunk on the association receive path.

sctp sf do 5 2 4 dupcook() issues SCTP CMD DELETE TCB for the temporary association, while the one the packet belongs to stays alive. A restarting peer can bundle DATA behind its COOKIE ECHO, so compare against chunk->asoc and leave that case alone.