CVE-2026-23125

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

sctp: move SCTP_CMD_ASSOC_SHKEY right after SCTP_CMD_PEER_INIT

A null-ptr-deref was reported in the SCTP transmit path when SCTP-AUTH key

initialization fails:

==================================================================

KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]

CPU: 0 PID: 16 Comm: ksoftirqd/0 Tainted: G W 6.6.0 #2

RIP: 0010:sctp_packet_bundle_auth net/sctp/output.c:264 [inline]

RIP: 0010:sctp_packet_append_chunk+0xb36/0x1260 net/sctp/output.c:401

Call Trace:

sctp_packet_transmit_chunk+0x31/0x250 net/sctp/output.c:189

sctp_outq_flush_data+0xa29/0x26d0 net/sctp/outqueue.c:1111

sctp_outq_flush+0xc80/0x1240 net/sctp/outqueue.c:1217

sctp_cmd_interpreter.isra.0+0x19a5/0x62c0 net/sctp/sm_sideeffect.c:1787

sctp_side_effects net/sctp/sm_sideeffect.c:1198 [inline]

sctp_do_sm+0x1a3/0x670 net/sctp/sm_sideeffect.c:1169

sctp_assoc_bh_rcv+0x33e/0x640 net/sctp/associola.c:1052

sctp_inq_push+0x1dd/0x280 net/sctp/inqueue.c:88

sctp_rcv+0x11ae/0x3100 net/sctp/input.c:243

sctp6_rcv+0x3d/0x60 net/sctp/ipv6.c:1127

The issue is triggered when sctp_auth_asoc_init_active_key() fails in

sctp_sf_do_5_1C_ack() while processing an INIT_ACK. In this case, the

command sequence is currently:

- SCTP_CMD_PEER_INIT

- SCTP_CMD_TIMER_STOP (T1_INIT)

- SCTP_CMD_TIMER_START (T1_COOKIE)

- SCTP_CMD_NEW_STATE (COOKIE_ECHOED)

- SCTP_CMD_ASSOC_SHKEY

- SCTP_CMD_GEN_COOKIE_ECHO

If SCTP_CMD_ASSOC_SHKEY fails, asoc->shkey remains NULL, while

asoc->peer.auth_capable and asoc->peer.peer_chunks have already been set by

SCTP_CMD_PEER_INIT. This allows a DATA chunk with auth = 1 and shkey = NULL

to be queued by sctp_datamsg_from_user().

Since command interpretation stops on failure, no COOKIE_ECHO should been

sent via SCTP_CMD_GEN_COOKIE_ECHO. However, the T1_COOKIE timer has already

been started, and it may enqueue a COOKIE_ECHO into the outqueue later. As

a result, the DATA chunk can be transmitted together with the COOKIE_ECHO

in sctp_outq_flush_data(), leading to the observed issue.

Similar to the other places where it calls sctp_auth_asoc_init_active_key()

right after sctp_process_init(), this patch moves the SCTP_CMD_ASSOC_SHKEY

immediately after SCTP_CMD_PEER_INIT, before stopping T1_INIT and starting

T1_COOKIE. This ensures that if shared key generation fails, authenticated

DATA cannot be sent. It also allows the T1_INIT timer to retransmit INIT,

giving the client another chance to process INIT_ACK and retry key setup.