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CVE-2026-89476
sctp: fix stream->outcnt underflow on duplicate RECONF responses
Published 2026-09-11 (37 days ago) by the Linux kernel CNA. Subsystem include/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-89476 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
A cached RECONF chunk may contain more than one request parameter. A duplicate response can therefore find and process the same ADD_OUT request again while another parameter is still outstanding, rolling back outcnt twice and possibly underflowing it. Track outstanding request types as bits and clear each bit after its first response. Later responses for the same request are then ignored.
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.
include/net/sctp/structs.h
net/sctp/stream.c
- What this is
- SCTP PROTOCOLMAINTAINERS section matched on include/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
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.70%, higher than 52.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- include/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.12 | 5.10.270 | 041f7df5a929 |
| 4.12 | 5.15.221 | 59f61c39cb99 |
| 4.12 | 6.1.188 | 793519e34386 |
| 4.12 | 6.6.157 | 092acd3c55a4 |
| 4.12 | 6.12.109 | 2d867663c563 |
| 4.12 | 6.18.50 | d02a5794c3de |
| 4.12 | 7.2.4 | 8320cbd81bc2 |
| 4.12 | 7.3 | 3faf13aff243 |
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’s RECONF chunk is processed by sctp_rcv() then sctp_sf_do_reconf() and sctp_process_strreset_resp() on an established association; kernel guidance treats in-kernel SCTP packet processing as Network.
- AC:LAttack complexity, low
- sctp_verify_reconf() allows two RESET_RESPONSE parameters in one chunk, so a peer can send two DENIED responses for the same ADD_OUT request_seq and reliably double-subtract outcnt; RECONF/add-streams being enabled is a deployment condition, not an uncontrolled race.
- PR:NPrivileges required, none
- The SCTP handshake and RECONF path require no credentials; AUTH is off by default and RECONF is not AUTH-gated, so any unauthenticated peer of a reachable association can send the triggering chunk.
- UI:NUser interaction, none
- No victim user action is required; duplicate RECONF responses are processed automatically in ESTABLISHED/SHUTDOWN_PENDING once the association has an outstanding multi-parameter ADD_STREAMS request.
- S:UScope, unchanged
- The oops and stream-count corruption stay inside the host kernel SCTP stack and do not cross a VM, IOMMU, or other security-authority boundary.
- C:NConfidentiality impact, none
- SCTP_SO() is genradix_ptr() and returns NULL past preallocated stream slots, so the underflow produces a NULL dereference rather than an out-of-bounds read or kernel memory disclosure.
- I:NIntegrity impact, none
- The double rollback corrupts the stream count then NULL-dereferences; ext pointers are cleared after kfree, so this is not a use-after-free write primitive or control-flow hijack.
- A:HAvailability impact, high
- A wrapped outcnt makes sctp_stream_free(), sendmsg, and other walkers dereference NULL SCTP_SO() slots, causing a kernel oops; extra-shrinking live streams also fails in-flight data, and the peer can abort to force teardown.