CVE-2026-90140

What the bug is

Since commit 053fc4f755ad ("fuse: fix UAF in rcu pathwalks"), fuse_conn_put() frees the fuse_conn through call_rcu() rather than synchronously. For cuse, fc->release is cuse_fc_release(), which lives in the cuse module. If the module is removed before the RCU grace period ends, the callback jumps into freed module memory: userspace / module unload | RCU softirq ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ close(/dev/cuse) | cuse_channel_release() | fuse_dev_release() | fuse_conn_put(fch->conn) | call_rcu(delayed_release) ------+---> callback queued | rmmod cuse | cuse_exit() | cuse_channel_destroy() | ... | return | | <module text freed> | | rcu_do_batch() | delayed_release() | fc->release() | -> cuse_fc_release() | ^^^ freed text! The freed module text is unmapped by vfree(), so the jump into the stale callback triggers a page-fault Oops. If the virtual address is subsequently reused, the callback could execute unrelated code (undefined behaviour). Fix this by calling rcu_barrier() in cuse_exit() so that any pending fuse_conn release callback completes before the module is removed.

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.

fs/fuse/cuse.c

What this is

FUSE FILESYSTEM [CORE]MAINTAINERS section matched on fs/fuse/ · fuse-devel@lists.linux.dev · Supported

Kernel module

cuse

Check it on the machine

grep -wE 'CONFIG_CUSE|CONFIG_FUSE_FS' /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 cuse

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, sid, bookworm · linux-6.12m

m

a loadable module on every flavour - check lsmod, can be blacklisted

Build switches

CONFIG_CUSE, CONFIG_FUSE_FS

Reads as

all on means the file is compiled; any one off means it is not.

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

2026-09-17 (31 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.21%, higher than 9.9% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

fs/fuse

Upstream fixes

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

Introduced	Fixed in	Commit
5.15.166	5.15.221	7fe415e1cd8f
6.1.107	6.1.188	45ae914b2f6e
6.6.48	6.6.157	ac5c49941338
6.8	6.12.110	a1b46aee33d8
6.8	6.18.52	389bd349ddbc
6.8	7.2.6	c40f3f24839f
6.8	7.3	4deb3edead0c

Debian advisories