# CVE-2026-53194: USB: serial: kl5kusb105: fix bulk-out buffer overflow

> A buffer overflow in the kl5kusb105 USB serial driver allows local attackers to trigger a slab out-of-bounds write, potentially leading to code execution or privilege escalation.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 25 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-53194, DEBIAN-CVE-2026-53194, GHSA-wwc5-7r8x-52gg, ROOT-OS-DEBIAN-11-CVE-2026-53194, ROOT-OS-DEBIAN-12-CVE-2026-53194, ROOT-OS-UBUNTU-2204-CVE-2026-53194, ROOT-OS-UBUNTU-2404-CVE-2026-53194, UBUNTU-CVE-2026-53194

## What is CVE-2026-53194?

CVE-2026-53194 is a high-severity memory corruption vulnerability in Linux kernel, published on 25 Jun 2026. 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:

USB: serial: kl5kusb105: fix bulk-out buffer overflow

klsi_105_prepare_write_buffer() is called by the generic write path
with the bulk-out buffer and its size (bulk_out_size, 64 bytes). It
stores a two-byte length header at the start of the buffer and copies
the payload from the write fifo starting at buf + KLSI_HDR_LEN, but
passes the full buffer size as the number of bytes to copy:

  count = kfifo_out_locked(&port->write_fifo, buf + KLSI_HDR_LEN,
                           size, &port->lock);

When the fifo holds at least size bytes, size bytes are copied starting
two bytes into the size-byte buffer, writing KLSI_HDR_LEN bytes past its
end. Copy at most size - KLSI_HDR_LEN bytes instead, leaving room for
the header as safe_serial already does.

Writing bulk_out_size or more bytes to the tty triggers a slab
out-of-bounds write, observed with KASAN by emulating the device with
dummy_hcd and raw-gadget:

  BUG: KASAN: slab-out-of-bounds in kfifo_copy_out+0x83/0xc0
  Write of size 64 at addr ffff888112c62202 by task python3
   kfifo_copy_out
   klsi_105_prepare_write_buffer [kl5kusb105]
   usb_serial_generic_write_start [usbserial]
  Allocated by task 139:
   usb_serial_probe [usbserial]
  The buggy address is located 2 bytes inside of allocated 64-byte region

The out-of-bounds write no longer occurs with this change applied.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-53194?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53194?

Apply the vendor's patch.

## Is CVE-2026-53194 being exploited?

There is no known exploitation of CVE-2026-53194 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-2026-53194 and fix it if it is affected.

What it is: CVE-2026-53194 is a high-severity memory corruption vulnerability in Linux kernel, published on 25 Jun 2026. 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-2026-53194 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-2026-53194/ (Markdown: https://insights.sbomify.com/CVE-2026-53194/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53194
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53194
- OSV: https://osv.dev/vulnerability/CVE-2026-53194

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53194/
Summaries are generated and may contain mistakes; the official description above is the record.