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CVE-2026-63942
parport: Fix race between port and client registration
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/parport. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63942 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 | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The parport subsystem registers port devices before they are fully initialised, resulting in a race condition where client drivers such as lp can attach to ports that are not completely initialised or even being torn down. When the port and client drivers are built as modules and loaded around the same time during boot, this occasionally results in a crash. I was able to make this happen reliably in a VM with a PC-style parallel port by patching parport_pc to fail probing: > --- a/drivers/parport/parport_pc.c > +++ b/drivers/parport/parport_pc.c > @@ -2069,7 +2069,7 @@ static struct parport *__parport_pc_probe_port(unsigned long int base, > if (!p) > goto out3; > > - base_res = request_region(base, 3, p->name); > + base_res = NULL; > if (!base_res) > goto out4; > and then running: while true; do modprobe lp & modprobe parport_pc wait rmmod lp parport_pc done for a few seconds. In the long term I think port registration should be changed to put the call to device_add() inside parport_announce_port(), but since the latter currently cannot fail this will require changing all port drivers. For now, add a flag to indicate whether a port has been "announced" and only try to attach client drivers to ports when the flag is set.
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/parport/share.c
include/linux/parport.h
- What this is
- PARALLEL PORT SUBSYSTEMMAINTAINERS section matched on drivers/parport/ · linux-parport@lists.infradead.org · Maintained
- Kernel module
- parport
Check it on the machine
grep -w CONFIG_PARPORT /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 parportPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64
- M
- a module where it is built at all; some flavours do not build it
- Build switch
- CONFIG_PARPORT
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
- 2026-07-19 (3 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
- 0.17%, higher than 5.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/parport
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.2 | 5.10.259 | f3378b0d7bd4 |
| 4.2 | 5.15.210 | 290f515c5e3b |
| 4.2 | 6.1.176 | d16548be2ea5 |
| 4.2 | 6.6.143 | 15b1723c1472 |
| 4.2 | 6.12.93 | 51026cff1f4f |
| 4.2 | 6.18.35 | 74d6aae1df45 |
| 4.2 | 7.0.12 | a1e81b58da01 |
| 4.2 | 7.1 | ef15ccbb3e86 |
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 reached only through local kernel module registration paths (init_module/finit_module/modprobe or built-in initcalls during boot), not via network or physical port I/O. An attacker must locally orchestrate concurrent loading of parport client and port drivers.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by concurrently loading/unloading `lp` (or `ppdev`) and `parport_pc`; the fix author reproduced this reliably with a tight modprobe/rmmod loop. Success does not depend on uncontrollable timing or memory layout.
- PR:LPrivileges required, low
- Triggering the race requires CAP_SYS_MODULE to load the relevant modules, which is obtainable by an unprivileged user in a user namespace on systems that permit it; it is not limited to irreducible init-namespace root.
- UI:NUser interaction, none
- Exploitation requires no victim interaction beyond the attacker's own module-load activity; boot-time crashes from parallel module loading also occur without user action.
- S:UScope, unchanged
- Impact is confined to kernel memory and availability within the same kernel security domain; there is no VM escape, sandbox breakout, or cross-authority boundary crossing.
- C:HConfidentiality impact, high
- Client drivers can attach while a port is partially initialized (e.g., NULL `port->dev` causing `device_add` failure) or actively being torn down after probe failure, creating a use-after-free window on the `parport` structure that can expose kernel memory.
- I:HIntegrity impact, high
- The same race window permits client attachment to ports with uninitialized or freed `parport_operations`/private data, enabling calls through invalid function pointers and heap corruption primitives consistent with control-flow hijacking.
- A:HAvailability impact, high
- Confirmed real-world kernel oops/panic during boot (Debian #1130365) with NULL instruction pointer, and the fix author demonstrated reliable crashes from the modprobe race loop.