CVE-2026-74586

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

sctp: clear new_transport when removing a peer

sctpprocessasconf_param() stores a newly added peer transport in

asoc->new_transport. After all parameters in the ASCONF chunk have been

processed, sctpsfdo_asconf() uses this pointer to send a HEARTBEAT to the

new transport.

An authenticated ASCONF from a remote SCTP peer can add a transport and

remove it again with a wildcard DEL-IP parameter in the same chunk. The

wildcard deletion preserves the transport on which the ASCONF arrived, but

removes the newly added transport through

sctpassocdelnonprimarypeers(). The removal does not clear

asoc->new_transport, leaving it pointing to the removed transport.

sctpsfdo_asconf() then creates a HEARTBEAT whose chunk->transport points

to the removed transport without holding a transport reference. During

local address replacement, srcoutofasocok keeps this HEARTBEAT on

controlchunklist. After the transport is freed by RCU, a successful

ASCONF_ACK for the replacement address releases the queued HEARTBEAT and

sctpoutqselect_transport() reads the freed transport's state.

The issue was found during a static audit of SCTP objects. With an

authenticated peer, the reproducer triggered the same KASAN report in 2

of 2 unpatched runs on a KASAN-enabled netdev/main kernel:

  BUG: KASAN: slab-use-after-free in sctpoutqselect_transport

  Read of size 4 at addr ffff88800b9bd95c by task python3/197

  Call Trace:

   sctpoutqselect_transport+0x549/0x8b0 [sctp]

   sctpoutqflush+0x306/0x2c60 [sctp]

   sctptransportimmediate_rtx+0xaf/0x260 [sctp]

   sctpprocessasconf_ack+0xa48/0xf70 [sctp]

  Allocated by task 197:

   sctptransportnew+0x68/0x650 [sctp]

   sctpassocadd_peer+0x258/0x12a0 [sctp]

   sctpprocessasconf+0x5e9/0x1090 [sctp]

  Last potentially related work creation:

   _callrcu_common.constprop.0+0x77/0xb70

   sctpassocdelnonprimarypeers+0x7c/0xd0 [sctp]

   sctpprocessasconf+0xd9c/0x1090 [sctp]

The first invalid access was a four-byte read of transport->state at

net/sctp/outqueue.c:833. The same reproducer completed the full

authenticated ASCONF and local-address replacement sequence with this

change without a KASAN report or oops.

Clear new_transport when its peer is removed, before it can be used to

create the HEARTBEAT.