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CVE-2026-89478
sctp: drop a chunk if its transport was removed
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem net/sctp. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89478 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6528-1 · 2026-09-29 · text | 6.12.111-1 | Update the kernel and reboot. DSA-6528-1 shipped the fix on 2026-09-29, in 6.12.111-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4817-1 · 2026-10-04 · text | 6.12.111-1~deb12u1 | Update the kernel and reboot. DLA-4817-1 shipped the fix on 2026-10-04, in 6.12.111-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
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.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/sctp/inqueue.c
- What this is
- SCTP PROTOCOLMAINTAINERS section matched on net/sctp/ · linux-sctp@vger.kernel.org · Maintained
- Kernel module
- sctp
Check it on the machine
grep -w CONFIG_IP_SCTP /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w sctpPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_IP_SCTP
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-11 (37 days ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.51%, higher than 42.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/sctp
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.12 | 5.10.270 | 3fc072e7cb4a |
| 2.6.12 | 5.15.221 | d7cb5ad83209 |
| 2.6.12 | 6.1.188 | 0422b092a3d4 |
| 2.6.12 | 6.6.157 | 928fd7920ba3 |
| 2.6.12 | 6.12.109 | c6c86a5e62a4 |
| 2.6.12 | 6.18.50 | 1035bdef1efb |
| 2.6.12 | 7.2.4 | 3537961df216 |
| 2.6.12 | 7.3 | 03a9d10ecf71 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DLA-4817-1 | 2026-10-04 | bookworm 6.12.111-1~deb12u1 | tracker |
| DSA-6528-1 | 2026-09-29 | trixie 6.12.111-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- A remote SCTP peer reaches the bug via received packets in sctp_rcv() on internet-facing SCTP servers and telecom endpoints; DATA that already resolved a transport is processed after an authenticated ASCONF DEL-IP (or COOKIE-ECHO restart) has removed that peer.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by sending ASCONF DEL-IP (or a restart that calls sctp_assoc_rm_peer) and a DATA chunk whose lookup already holds the doomed transport; the backlog path is FIFO-deterministic while the socket is in a syscall, and the direct path is a bh_lock_sock race the attacker creates.
- PR:NPrivileges required, none
- Exploitation requires only a network-reachable established SCTP association; no local Linux credentials, capabilities, or namespaces are needed, and SCTP-AUTH keys used for ASCONF come from the handshake the peer itself performs.
- UI:NUser interaction, none
- Inbound SCTP packets are processed automatically in softirq or socket backlog on a listening or already-associated endpoint; no victim user action such as opening a file or mounting a device is required.
- S:UScope, unchanged
- Impact is kernel memory corruption and potential privilege escalation within the host SCTP stack; it does not cross a VM, IOMMU, or other security-authority boundary.
- C:HConfidentiality impact, high
- DATA processing plants the removed transport into asoc->peer.last_data_from; after the lookup reference is dropped the object is RCU-freed, and the next delayed SACK dereferences the freed sctp_transport in sctp_outq_select_transport(), a UAF that enables arbitrary kernel disclosure via heap grooming.
- I:HIntegrity impact, high
- sctp_outq_select_transport() does list_add_tail() into the freed send_ready field, and sctp_packet_config()/sctp_transport_burst_limited() write vtag, pathmtu, cwnd, and burst_limited into the reclaimed slab object, yielding arbitrary write and control-flow hijack primitives.
- A:HAvailability impact, high
- Dereferencing the freed transport during delayed SACK transmission can immediately oops or panic the kernel, and the UAF can be triggered repeatedly by a malicious SCTP peer.