CVE-2026-89478
moderateUse-after-free in Linux kernel SCTP stack via ASCONF DEL-IP transport removal
A use-after-free exists in the Linux kernel's SCTP implementation where a packet's transport pointer can outlive the transport itself. When an authenticated SCTP peer sends an ASCONF DEL-IP that removes a transport while a packet referencing that transport is sitting on the socket backlog or between the lookup and socket lock, a DATA chunk in that packet re-inserts the dead transport into the association's last_data_from state; once the transport is freed via RCU, the next delayed SACK carries the dangling pointer and sctp_outq_select_transport() reads freed memory. An attacker must be an authenticated peer of an SCTP association, which limits the attacker pool but enables remote exploitation with no additional privileges or user interaction. The CVSS 3.1 base score of 9.8 reflects potential high impact on confidentiality, integrity, and availability, though the most direct observed consequence is memory corruption likely resulting in a kernel crash or denial of service. Affected systems are any Linux machines loading the SCTP stack (sctp.ko) that terminate SCTP associations with untrusted or semi-trusted peers, most notably telecom signaling nodes. No public proof of concept is known and the flaw is not listed in CISA's KEV catalog.
What to do: Apply a kernel update that includes the sctp fix (drop chunk when transport was removed) as soon as your distribution ships it. If SCTP is not required, blacklist the sctp kernel module and block SCTP (protocol 132) at perimeter firewalls. Operators of SCTP-terminating telecom infrastructure should verify peer authentication policy and watch for unexpected kernel crashes or oopses in sctp_outq_select_transport().
| Linux kernel (SCTP stack) | — |
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
In the Linux kernel, the following vulnerability has been resolved: sctp: drop a chunk if its transport was removed sctp_rcv() resolves the transport once per packet and leaves it in chunk->transport. The lookup reference, or the one sctp_add_backlog() takes if the socket is owned by userspace, keeps it around until the chunk has been processed. An authenticated ASCONF DEL-IP can remove it in the meantime. sctp_assoc_rm_peer() takes the transport out of the association and calls sctp_transport_free(), which tags it dead and drops the reference the association held. There is a window on both paths: the packet can sit on the socket backlog, and on the direct path the lookup completes before bh_lock_sock(). The DATA chunk in that packet puts the removed transport back into asoc->peer.last_data_from. Once the packet is done that reference goes away and the transport is freed by RCU, so the next delayed SACK carries the pointer into the SACK chunk and sctp_outq_select_transport() reads the freed transport's state. Drop the chunk in sctp_inq_push(), next to the existing rcvr->dead check. Both paths reach it with the association's socket lock held. The peer retransmits it.
- Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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