# CVE-2025-68335: comedi: pcl818: fix null-ptr-deref in pcl818_ai_cancel()

> A null pointer dereference in the Linux kernel's pcl818 driver allows local attackers to cause a system crash via device detachment.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-68335, DEBIAN-CVE-2025-68335, GHSA-7r9r-9pcc-36g7, ROOT-OS-DEBIAN-11-CVE-2025-68335, ROOT-OS-DEBIAN-12-CVE-2025-68335, ROOT-OS-DEBIAN-13-CVE-2025-68335, ROOT-OS-UBUNTU-2204-CVE-2025-68335, ROOT-OS-UBUNTU-2404-CVE-2025-68335, UBUNTU-CVE-2025-68335

## What is CVE-2025-68335?

CVE-2025-68335 is a vulnerability in Linux, published on 22 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

comedi: pcl818: fix null-ptr-deref in pcl818_ai_cancel()

Syzbot identified an issue [1] in pcl818_ai_cancel(), which stems from
the fact that in case of early device detach via pcl818_detach(),
subdevice dev->read_subdev may not have initialized its pointer to
&struct comedi_async as intended. Thus, any such dereferencing of
&s->async->cmd will lead to general protection fault and kernel crash.

Mitigate this problem by removing a call to pcl818_ai_cancel() from
pcl818_detach() altogether. This way, if the subdevice setups its
support for async commands, everything async-related will be
handled via subdevice's own ->cancel() function in
comedi_device_detach_locked() even before pcl818_detach(). If no
support for asynchronous commands is provided, there is no need
to cancel anything either.

[1] Syzbot crash:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
CPU: 1 UID: 0 PID: 6050 Comm: syz.0.18 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:pcl818_ai_cancel+0x69/0x3f0 drivers/comedi/drivers/pcl818.c:762
...
Call Trace:
 <TASK>
 pcl818_detach+0x66/0xd0 drivers/comedi/drivers/pcl818.c:1115
 comedi_device_detach_locked+0x178/0x750 drivers/comedi/drivers.c:207
 do_devconfig_ioctl drivers/comedi/comedi_fops.c:848 [inline]
 comedi_unlocked_ioctl+0xcde/0x1020 drivers/comedi/comedi_fops.c:2178
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
...

## Which versions are affected by CVE-2025-68335?


## How do I fix CVE-2025-68335?

Apply the vendor's patch.

## Is CVE-2025-68335 being exploited?

There is no known exploitation of CVE-2025-68335 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-68335 and fix it if it is affected.

What it is: CVE-2025-68335 is a vulnerability in Linux, published on 22 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-68335 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-68335/ (Markdown: https://insights.sbomify.com/CVE-2025-68335/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-68335
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-68335
- OSV: https://osv.dev/vulnerability/CVE-2025-68335

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-68335/
Summaries are generated and may contain mistakes; the official description above is the record.