Linux Kernel SCTP Dereferences a NULL Transport on Untransmitted Stream Reconfiguration Completion, Reachable by a Remote Peer

Status: NEW  |  Advisory ID: CVE-2026-89477

Key Details

What to Know

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

sctp: fix NULL deref on untransmitted RECONF completion

sctp_process_strreset_outreq(), sctp_process_strreset_addstrm_out() and

sctp_process_strreset_resp() complete a pending stream reconfiguration

request by stopping the reconf timer on the transport it was sent on:

t = asoc->strreset_chunk->transport;

if (timer_delete(&t->reconf_timer))

sctp_transport_put(t);

chunk->transport is assigned by __sctp_packet_append_chunk() when the

chunk is appended to an outbound packet, and sctp_outq_flush_ctrl() arms

the reconf timer at that same point. A request already published in

asoc->strreset_chunk but not yet transmitted has neither, so completing

it dereferences NULL.

Two ways to get there. sctp_send_asconf_del_ip() sets

asoc->src_out_of_asoc_ok without sending anything when the address being

removed is the association's last one, and sctp_outq_flush_ctrl() then

leaves every non-ASCONF control chunk queued; as only

sctp_process_asconf_ack() clears that flag, it persists. An unprivileged

process that removes such an address and then asks for a stream reset

panics the kernel from softirq. A peer needs neither ASCONF nor local

help: sctp_cmd_interpreter() uncorks the outqueue only once the whole

packet has been processed, so a reply built while walking a RECONF chunk

stays untransmitted for the rest of that walk, and one RECONF chunk

carrying [Incoming SSN Reset Request, Outgoing SSN Reset Request,

Response] -- or two RECONF chunks in one packet -- reaches the same

dereference.

KASAN: null-ptr-deref in range [0x00000000000001e8-0x00000000000001ef]

RIP: 0010:timer_delete+0x67/0x110

Call Trace:

<IRQ>

sctp_process_strreset_addstrm_out (net/sctp/stream.c:832)

sctp_sf_do_reconf (net/sctp/sm_statefuns.c:4212)

sctp_do_sm (net/sctp/sm_sideeffect.c:1172)

sctp_assoc_bh_rcv (net/sctp/associola.c:1044)

sctp_rcv (net/sctp/input.c:243)

ip_local_deliver (net/ipv4/ip_input.c:262)

process_backlog (net/core/dev.c:6680)

</IRQ>

A response can only acknowledge a request that was actually sent, so do

not match asoc->strreset_chunk while chunk->transport is NULL. Guarding

the lookup covers all three completion sites. (NVD)

References