Description
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.
Published: 2026-08-22
Score: n/a
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Sat, 22 Aug 2026 15:45:00 +0000

Type Values Removed Values Added
Description 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.
Title sctp: clear new_transport when removing a peer
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-08-22T15:31:39.094Z

Reserved: 2026-08-15T05:44:03.918Z

Link: CVE-2026-74586

cve-icon Vulnrichment

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