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CVE-2026-74688
sctp: clear control chunk transport if it is being removed
Published 2026-08-22 (2 months 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-2026-74688 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
sctp_make_heartbeat_ack() caches the destination transport in chunk->transport without taking a reference. When src_out_of_asoc_ok is enabled, the HEARTBEAT ACK may remain queued on control_chunk_list instead of being transmitted immediately. If the peer transport is removed while the chunk is still queued, sctp_assoc_rm_peer() drops the transport and schedules it for RCU freeing, but only clears cached transport pointers in out_chunk_list. The queued control chunk therefore retains a dangling transport pointer. Once an ASCONF_ACK clears the suppression and the queued control chunk is transmitted, SCTP dereferences the stale transport pointer, leading to a use-after-free. Fix this by also clearing chunk->transport for queued control chunks in control_chunk_list when removing the transport.
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/associola.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
- 2026-08-22 (2 months 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
- 0.50%, higher than 41.5% 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 |
|---|---|---|
| 3.1 | 5.10.265 | dbb3f418a866 |
| 3.1 | 5.15.216 | fad4766a7422 |
| 3.1 | 6.1.183 | 936658ec41c2 |
| 3.1 | 6.6.152 | 8de65194a04d |
| 3.1 | 6.12.104 | 6160e756db81 |
| 3.1 | 6.18.45 | 18d704bdd809 |
| 3.1 | 7.1.9 | 4d6b9cac6df5 |
| 3.1 | 7.2 | c9158ceaf277 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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
- The bug is reached from remotely received SCTP packets (HEARTBEAT, ASCONF, ASCONF_ACK) processed in sctp_rcv() and the association input state machine on internet-facing SCTP servers and telecom endpoints.
- AC:LAttack complexity, low
- A remote SCTP peer controls packet sequencing and can send HEARTBEAT while src_out_of_asoc_ok blocks transmission, remove transports via ASCONF DEL_IP, then trigger flush when ASCONF_ACK clears suppression.
- PR:NPrivileges required, none
- Exploitation requires only a network-reachable established SCTP association; the attacker needs no Linux credentials, capabilities, or namespaces—only the ability to send valid SCTP traffic to the target.
- UI:NUser interaction, none
- No victim user action is required; the use-after-free is triggered entirely by SCTP protocol messages sent by a remote peer during normal association operation or address migration.
- S:UScope, unchanged
- Impact is confined to kernel memory corruption and privilege escalation within the host kernel; it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- Stale chunk->transport pointers dereference RCU-freed sctp_transport objects in sctp_outq_select_transport() and sctp_packet_transmit(), a use-after-free that enables arbitrary kernel memory disclosure via heap grooming.
- I:HIntegrity impact, high
- Use-after-free of sctp_transport allows controlled reuse of freed kmalloc objects, providing a standard path to arbitrary kernel writes and local privilege escalation or remote code execution in kernel context.
- A:HAvailability impact, high
- Dereferencing the freed transport during control-chunk transmission can immediately kernel oops or panic the system; use-after-free bugs inherently threaten availability even when full exploitation is not attempted.