CVE-2025-21689 USB: serial: quatech2: fix null-ptr-deref in qt2_process_read_urb()

What is CVE-2025-21689?

CVE-2025-21689 is a medium-severity vulnerability in Linux kernel, published on 10 Feb 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:

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.

Weakness: CWE-476

Which versions are affected by CVE-2025-21689?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-21689?

Apply the vendor's patch.

Is CVE-2025-21689 being exploited?

There is no known exploitation of CVE-2025-21689 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2025-21689, DEBIAN-CVE-2025-21689, GHSA-mgqg-wqxj-q43c, UBUNTU-CVE-2025-21689.