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CVE-2026-74586
sctp: clear new_transport when removing a peer
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-2026-74586 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_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.
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 |
|---|---|---|
| 3.2 | 5.10.265 | c0f973bb5118 |
| 3.2 | 5.15.216 | 3b539b317cd0 |
| 3.2 | 6.1.183 | db9d8e3b670f |
| 3.2 | 6.6.152 | 31efa656cf6a |
| 3.2 | 6.12.104 | 291accf36feb |
| 3.2 | 6.18.45 | ca33df36aa01 |
| 3.2 | 7.1.9 | 163847552a57 |
| 3.2 | 7.2 | beb33f8ee1ca |
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 triggered when a remote SCTP peer sends an authenticated ASCONF chunk that is processed via sctp_rcv() through the state machine into sctp_sf_do_asconf() and sctp_process_asconf(); this is standard network packet handling, not a local syscall or ioctl path.
- AC:LAttack complexity, low
- The remote peer fully controls a single ASCONF containing ADD_IP followed by wildcard DEL-IP to add then remove a transport while leaving asoc->new_transport dangling; combined with routine SCTP local address replacement (src_out_of_asoc_ok), the KASAN reproducer hit the UAF in 2/2 runs.
- PR:NPrivileges required, none
- Exploitation requires only being an established SCTP association peer sending SCTP-AUTH-protected ASCONF traffic negotiated during the normal handshake (or addip_noauth); no Linux account, capability, or init-namespace privilege is needed on the victim host.
- UI:NUser interaction, none
- No victim user action such as opening a file or mounting a filesystem is required; the kernel automatically processes attacker-crafted ASCONF packets on an existing SCTP association during normal server operation.
- S:UScope, unchanged
- Impact is confined to kernel heap corruption on the vulnerable host (slab UAF on sctp_transport) and potential privilege escalation within that kernel; it does not cross VM, container, or IOMMU security boundaries.
- C:HConfidentiality impact, high
- KASAN reports slab-use-after-free with a 4-byte read of freed sctp_transport->state in sctp_outq_select_transport(); UAF on heap transport objects enables grooming for arbitrary kernel memory disclosure per kernel CVSS guidance.
- I:HIntegrity impact, high
- The dangling sctp_transport pointer is embedded in a queued HEARTBEAT control chunk without a reference; UAF on this heap object can be leveraged via heap spraying for arbitrary kernel writes and control-flow hijacking, not merely a bounded corruption.
- A:HAvailability impact, high
- Dereferencing the freed transport during sctp_outq_flush() causes a reproducible kernel UAF/oops; remote peers can repeatedly trigger this against SCTP endpoints handling ADD-IP traffic, yielding denial of service or crash.