CVE-2026-74587

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

sctp: fix use-after-free of cached ASCONF chunk

addiplastasconf caches the outstanding outbound ASCONF chunk. The normal

ASCONF-ACK completion path releases the chunk and clears the pointer.

However, sctpasconfqueue_teardown() releases the cached chunk without

clearing addiplastasconf. During peer restart handling,

sctpsfdodupcooka() queues SCTPCMDPURGEASCONFQUEUE, which invokes

sctpasconfqueue_teardown() while the association remains alive and leaves

the pointer dangling.

A delayed authenticated ASCONF-ACK can then reach sctpsfdoasconfack(),

which accesses the stale chunk and passes it to sctpprocessasconf_ack(),

causing a use-after-free and a second release.

Clearing the pointer exposes a race with T4 expiry. Peer restart handling

queues the timer stop before the purge, but SCTPCMDTIMER_STOP uses

timer_delete(), which does not wait for a callback already running on

another CPU. Such a callback can reach sctpsft4timerexpire() after

the purge and dereference NULL.

Clear addiplastasconf after releasing the cached chunk, and make

sctpsft4timerexpire() consume a stale T4 expiry if no outstanding

ASCONF remains.