CVE-2026-89478: sctp: drop a chunk if its transport was removed
In the Linux kernel, the following vulnerability has been resolved:
sctp: drop a chunk if its transport was removed
sctprcv() resolves the transport once per packet and leaves it in chunk->transport. The lookup reference, or the one sctpaddbacklog() takes if the socket is owned by userspace, keeps it around until the chunk has been processed.
An authenticated ASCONF DEL-IP can remove it in the meantime. sctpassocrmpeer() takes the transport out of the association and calls sctptransportfree(), which tags it dead and drops the reference the association held. There is a window on both paths: the packet can sit on the socket backlog, and on the direct path the lookup completes before bhlocksock().
The DATA chunk in that packet puts the removed transport back into asoc->peer.lastdatafrom. Once the packet is done that reference goes away and the transport is freed by RCU, so the next delayed SACK carries the pointer into the SACK chunk and sctpoutqselecttransport() reads the freed transport's state.
Drop the chunk in sctpinqpush(), next to the existing rcvr->dead check. Both paths reach it with the association's socket lock held. The peer retransmits it.
Affected Software
Event History
Frequently Asked Questions
What conditions are required for this issue to be triggered?
The association must accept an authenticated ASCONF DEL-IP request that removes a peer transport while an SCTP packet referencing that transport is still awaiting processing. The affected packet can be queued on the socket backlog or can be in the direct receive path before the socket lock is acquired.
What happens after the transport is removed?
A DATA chunk from the already-received packet can restore the removed transport pointer in the association's last_data_from field. After its reference is released and RCU frees the transport, a later delayed SACK can use that stale pointer and read freed transport state.
Is packet loss expected from the fix?
The fix drops chunks whose transport has been removed. The peer is expected to retransmit the dropped chunk.