# CVE-2023-53523: can: gs_usb: fix time stamp counter initialization

> A race condition in the gs_usb CAN driver causes a null pointer dereference, leading to a kernel crash when unloading the driver.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **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:** 1 Oct 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-53523, DEBIAN-CVE-2023-53523, GHSA-67pq-6gr2-gqmr, ROOT-OS-DEBIAN-12-CVE-2023-53523, UBUNTU-CVE-2023-53523

## What is CVE-2023-53523?

CVE-2023-53523 is a medium-severity vulnerability in Linux kernel, published on 1 Oct 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:

can: gs_usb: fix time stamp counter initialization

If the gs_usb device driver is unloaded (or unbound) before the
interface is shut down, the USB stack first calls the struct
usb_driver::disconnect and then the struct net_device_ops::ndo_stop
callback.

In gs_usb_disconnect() all pending bulk URBs are killed, i.e. no more
RX'ed CAN frames are send from the USB device to the host. Later in
gs_can_close() a reset control message is send to each CAN channel to
remove the controller from the CAN bus. In this race window the USB
device can still receive CAN frames from the bus and internally queue
them to be send to the host.

At least in the current version of the candlelight firmware, the queue
of received CAN frames is not emptied during the reset command. After
loading (or binding) the gs_usb driver, new URBs are submitted during
the struct net_device_ops::ndo_open callback and the candlelight
firmware starts sending its already queued CAN frames to the host.

However, this scenario was not considered when implementing the
hardware timestamp function. The cycle counter/time counter
infrastructure is set up (gs_usb_timestamp_init()) after the USBs are
submitted, resulting in a NULL pointer dereference if
timecounter_cyc2time() (via the call chain:
gs_usb_receive_bulk_callback() -> gs_usb_set_timestamp() ->
gs_usb_skb_set_timestamp()) is called too early.

Move the gs_usb_timestamp_init() function before the URBs are
submitted to fix this problem.

For a comprehensive solution, we need to consider gs_usb devices with
more than 1 channel. The cycle counter/time counter infrastructure is
setup per channel, but the RX URBs are per device. Once gs_can_open()
of _a_ channel has been called, and URBs have been submitted, the
gs_usb_receive_bulk_callback() can be called for _all_ available
channels, even for channels that are not running, yet. As cycle
counter/time counter has not set up, this will again lead to a NULL
pointer dereference.

Convert the cycle counter/time counter from a "per channel" to a "per
device" functionality. Also set it up, before submitting any URBs to
the device.

Further in gs_usb_receive_bulk_callback(), don't process any URBs for
not started CAN channels, only resubmit the URB.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2023-53523?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-53523?

Apply the vendor's patch.

## Is CVE-2023-53523 being exploited?

There is no known exploitation of CVE-2023-53523 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-53523 and fix it if it is affected.

What it is: CVE-2023-53523 is a medium-severity vulnerability in Linux kernel, published on 1 Oct 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-2023-53523 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2023-53523/ (Markdown: https://insights.sbomify.com/CVE-2023-53523/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-53523
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-53523
- OSV: https://osv.dev/vulnerability/CVE-2023-53523

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-53523/
Summaries are generated and may contain mistakes; the official description above is the record.