CVE-2026-72025

What the bug is

When data buffers are reused, e.g. for interval sample records, the first record determines the data length, and the size of the buffer for user copy. Current monwriter code does not check if the data length was changed for subsequent records, which also would never happen for valid user programs. However, a malicious user could change the data length, resulting in out of bounds user copy to the kernel buffer, and memory corruption. By default, the monwriter misc device is created with root-only permissions, so practical impact is typically low. Fix this by checking for changed data length and rejecting such records.

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.

drivers/s390/char/monwriter.c

What this is

S390 ARCHITECTUREMAINTAINERS section matched on drivers/s390/ · linux-s390@vger.kernel.org · Supported

Kernel module

monwriter

Check it on the machine

grep -wE 'CONFIG_MONWRITER|CONFIG_S390' /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 monwriter

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 does not build this code in 1 release. It does build it in 3 releases, so the answer depends on which release the machine runs.

• bookwormn
• trixieMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt/amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt/arm64, armel/rpi, armhf/armmp, armhf/armmp-lpae, armhf/rt/armmp, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64
• forky, sidMnot built on amd64/amd64, amd64/cloud-amd64, amd64/rt-amd64, arm64/arm64, arm64/arm64-16k, arm64/cloud-arm64, arm64/rt-arm64, armhf/armmp, armhf/armmp-lpae, loong64/loong64, ppc64el/powerpc64le, ppc64el/powerpc64le-64k, riscv64/riscv64

n

not enabled on any flavour - this release does not build the code

M

a module where it is built at all; some flavours do not build it

Build switches

CONFIG_MONWRITER, CONFIG_S390

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

2026-08-15 (2 months ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.22%, higher than 11.3% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

drivers/s390

Upstream fixes

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

Introduced	Fixed in	Commit
2.6.19	5.10.261	096dff124703
2.6.19	5.15.212	d39cf4a6d721
2.6.19	6.1.178	759d91378203
2.6.19	6.6.145	036bc5661060
2.6.19	6.12.97	01f3ce411711
2.6.19	6.18.40	f0745496f7c1
2.6.19	7.1.5	ae5347f3db17
2.6.19	7.2	2995ccec260c