Look up another CVE · open CVE-2026-53070 in the interactive tracker

CVE-2026-53070

sctp: disable BH before calling udp_tunnel_xmit_skb()

7.5 EPSS 0.3% AV:N

Published 2026-06-24 (4 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-2026-53070 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	vulnerable	6.1.190-1	No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication.
Debian 13trixie	fixedDSA-6381-1 · 2026-07-05 · text	6.12.95-1	Update the kernel and reboot. DSA-6381-1 shipped the fix on 2026-07-05, in 6.12.95-1. A running kernel keeps the old code until the machine restarts.
Debian 14forky	fixed	7.0.10-1	Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts.
Debian unstablesid	fixed	7.0.10-1	Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts.

The vulnerability

What the bug is

udp_tunnel_xmit_skb() / udp_tunnel6_xmit_skb() are expected to run with BH disabled. After commit 6f1a9140ecda ("add xmit recursion limit to tunnel xmit functions"), on the path: udp(6)_tunnel_xmit_skb() -> ip(6)tunnel_xmit() dev_xmit_recursion_inc()/dec() must stay balanced on the same CPU. Without local_bh_disable(), the context may move between CPUs, which can break the inc/dec pairing. This may lead to incorrect recursion level detection and cause packets to be dropped in ip(6)_tunnel_xmit() or __dev_queue_xmit(). Fix it by disabling BH around both IPv4 and IPv6 SCTP UDP xmit paths. In my testing, after enabling the SCTP over UDP: # ip net exec ha sysctl -w net.sctp.udp_port=9899 # ip net exec ha sysctl -w net.sctp.encap_port=9899 # ip net exec hb sysctl -w net.sctp.udp_port=9899 # ip net exec hb sysctl -w net.sctp.encap_port=9899 # ip net exec ha iperf3 -s - without this patch: # ip net exec hb iperf3 -c 192.168.0.1 --sctp [ 5] 0.00-10.00 sec 37.2 MBytes 31.2 Mbits/sec sender [ 5] 0.00-10.00 sec 37.1 MBytes 31.1 Mbits/sec receiver - with this patch: # ip net exec hb iperf3 -c 192.168.0.1 --sctp [ 5] 0.00-10.00 sec 3.14 GBytes 2.69 Gbits/sec sender [ 5] 0.00-10.00 sec 3.14 GBytes 2.69 Gbits/sec receiver

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/ipv6.c
net/sctp/protocol.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 sctp

Prints 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, sidm

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

Debian tracker CVE record NVD kernel CNA record

Signals

Published: 2026-06-24 (4 months 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: 0.35%, higher than 26.6% 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
5.11	6.12.95	be3bfcb34bda
5.11	6.18.37	0de7db2eb27e
5.11	7.0.10	790093245e35
5.11	7.1	2cd7e6971fc2

Debian advisories

Advisory	Date	Shipped to	Debian
DSA-6381-1	2026-07-05	trixie 6.12.95-1	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: SCTP-over-UDP transmit is reachable from network-facing SCTP endpoints when received packets or application-level requests cause replies through the SCTP output path. A remote peer can trigger the affected UDP-encapsulated transmit path in a reasonable SCTP service deployment.
AC:LAttack complexity, low: The bug is triggered by repeatedly causing SCTP-over-UDP transmission in process/backlog context where BH is not disabled. Although CPU migration/preemption timing is involved, the attacker can drive repeated transmissions and the higher-severity choice is AC:L.
PR:NPrivileges required, none: A remote SCTP peer does not need local credentials or kernel privileges to send packets to an SCTP-over-UDP service and induce responses. Local setup of SCTP-over-UDP may require configuration, but exploitation of an exposed configured service is unauthenticated.
UI:NUser interaction, none: No victim user action is required once an SCTP-over-UDP endpoint is exposed. The attacker only sends network traffic.
S:UScope, unchanged: The impact remains within the kernel networking stack and host network availability. This is not a VM escape, IOMMU bypass, or cross-authority boundary violation.
C:NConfidentiality impact, none: The bug corrupts transmit recursion accounting, not packet contents or attacker-readable memory. I found no evidence of an information disclosure primitive.
I:NIntegrity impact, none: The issue causes incorrect recursion detection and packet drops, not arbitrary writes, control-flow hijack, or attacker-controlled data modification. The only modified state is internal transmit recursion accounting.
A:HAvailability impact, high: Unbalanced per-CPU transmit recursion counters can become stale or underflowed, causing false recursion-limit detection and persistent packet drops in tunnel or device transmit paths. Repeated triggering can deny network availability for affected SCTP-over-UDP traffic and potentially broader transmit paths on affected CPUs.