Look up another CVE · open CVE-2026-74262 in the interactive tracker

CVE-2026-74262

kcm: use WRITE_ONCE() when changing lower socket callbacks

7.8 EPSS 0.2% AV:L

Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/kcm. Debian urgency: not yet assigned.

What to do, per Debian release

Debian's own status for CVE-2026-74262 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	fixed	6.1.180-1	Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts.
Debian 13trixie	fixed	6.12.100-1	Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts.
Debian 14forky	fixed	7.1.5-1	Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts.
Debian unstablesid	fixed	7.1.5-1	Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts.

The vulnerability

What the bug is

kcm_attach() replaces a live lower TCP socket's sk_data_ready and sk_write_space callbacks with KCM handlers, and kcm_unattach() restores them later. Those callback-pointer updates are still plain stores even though the same fields can be read and invoked concurrently on other CPUs. If another CPU observes an older callback snapshot after the live field has already been restored, callback execution can run with a mismatched target and sk_user_data state, leading to stale or misdirected wakeups. Use WRITE_ONCE() for the callback replacement and restore operations so these shared callback fields follow the same visibility contract already established by the earlier 4022 fixes.

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/kcm/kcmsock.c

What this is: NETWORKING [GENERAL]MAINTAINERS section matched on net/ · netdev@vger.kernel.org · Maintained
Kernel module: kcm

Check it on the machine

grep -w CONFIG_AF_KCM /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 kcm

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_AF_KCM

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: 2026-08-15 (2 months ago)source
CVSS: 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it
Attack vector: local (AV:L)source
EPSS: 0.18%, higher than 7.6% of all CVEssource
CISA KEV: not listedthe KEV catalogue
Debian urgency: not yet assignedsource
Subsystem: net/kcm

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
4.6	5.10.261	0cb3e2f40679
4.6	5.15.212	fa26e4606aed
4.6	6.1.178	b4ccd6eef671
4.6	6.6.145	b8c90823cdfb
4.6	6.12.97	11faefd11ce2
4.6	6.18.40	f01fb6138f8e
4.6	7.1.5	9684fff87124
4.6	7.2	47186409c092

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:LAttack vector, local: The bug is in kcm_attach()/kcm_unattach() callback replacement reachable only via local socket()/ioctl(SIOCKCMATTACH/UNATTACH); remote TCP can trigger callback invocation but cannot perform attach/detach without local access to the KCM socket.
AC:LAttack complexity, low: The attacker controls both sides of the race by concurrently issuing attach/unattach ioctls while driving RX/TX on the same TCP socket to provoke READ_ONCE(sk_data_ready/sk_write_space) on other CPUs during callback pointer transitions.
PR:LPrivileges required, low: No capability checks exist in KCM; any local user who can create AF_KCM sockets and load a BPF_PROG_TYPE_SOCKET_FILTER program (allowed without CAP_BPF on many systems, or via user-namespace capabilities) can reach the vulnerable ioctl path.
UI:NUser interaction, none: Exploitation requires only attacker-controlled local socket operations and concurrent network I/O; no victim user or administrator action is needed beyond the attacker using their own sockets.
S:UScope, unchanged: Impact is kernel memory corruption and privilege escalation within the same security authority; this is not a cross-boundary escape such as guest-to-host VM breakout or IOMMU bypass.
C:HConfidentiality impact, high: Plain stores to sk_data_ready/sk_write_space can desynchronize from sk_user_data, letting stale KCM callbacks dereference freed or mismatched kcm_psock/strparser state and leak attacker-influenced kernel heap contents.
I:HIntegrity impact, high: Misdirected psock_write_space/psock_data_ready on dangling kcm_psock can corrupt heap metadata and queue_work on freed kcm_sock objects, enabling control-flow hijack and arbitrary kernel write primitives.
A:HAvailability impact, high: The data race causes use-after-free and invalid pointer dereferences in softirq/workqueue callback paths, producing reliable kernel oops/panic or hang even when full exploitation is not achieved.