sctp: clear new_transport when removing a peer

Summary

In the Linux kernel, the following vulnerability has been resolved: sctp: clear new_transport when removing a peer sctp_process_asconf_param() stores a newly added peer transport in asoc->new_transport. After all parameters in the ASCONF chunk have been processed, sctp_sf_do_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 sctp_assoc_del_nonprimary_peers(). The removal does not clear asoc->new_transport, leaving it pointing to the removed transport. sctp_sf_do_asconf() then creates a HEARTBEAT whose chunk->transport points to the removed transport without holding a transport reference. During local address replacement, src_out_of_asoc_ok keeps this HEARTBEAT on control_chunk_list. After the transport is freed by RCU, a successful ASCONF_ACK for the replacement address releases the queued HEARTBEAT and sctp_outq_select_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 sctp_outq_select_transport Read of size 4 at addr ffff88800b9bd95c by task python3/197 Call Trace: sctp_outq_select_transport+0x549/0x8b0 [sctp] sctp_outq_flush+0x306/0x2c60 [sctp] sctp_transport_immediate_rtx+0xaf/0x260 [sctp] sctp_process_asconf_ack+0xa48/0xf70 [sctp] Allocated by task 197: sctp_transport_new+0x68/0x650 [sctp] sctp_assoc_add_peer+0x258/0x12a0 [sctp] sctp_process_asconf+0x5e9/0x1090 [sctp] Last potentially related work creation: __call_rcu_common.constprop.0+0x77/0xb70 sctp_assoc_del_nonprimary_peers+0x7c/0xd0 [sctp] sctp_process_asconf+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.

Timeline

1. Aug 22, 2026, 3:31 PM UTCCVE published
2. Oct 16, 2026, 7:01 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: yes · Technical impact: total

3. Oct 16, 2026, 7:05 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in c0f973bb5118dd1b146cda3fcc8af6f6057befec; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in 3b539b317cd052236fed0350364ff1268996ba46; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in db9d8e3b670f841755bc2018f178472dc6064d27; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in 31efa656cf6aface26e88f038c14f22ee6ca1500; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in 291accf36febce751021888de5f15090f4875b56; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in ca33df36aa0143a1d04f57d2086020c12e7eddb7; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in 163847552a571bd55094291f4ffcdc1de0f14a7b; From 6af29ccc223b0feb6fc6112281c3fa3cdb1afddf · fixed in beb33f8ee1ca83acddb2a5ae80f3d22ec550b4c3

• Linux Linux

  3.2

• KernelLinux

  From 3.2.0 · fixed in 5.10.265; From 5.11.0 · fixed in 5.15.216; From 5.16.0 · fixed in 6.1.183; From 6.2.0 · fixed in 6.6.152; From 6.7.0 · fixed in 6.12.104; From 6.13.0 · fixed in 6.18.45; From 6.19.0 · fixed in 7.1.9

References 8