CVE-2025-21704: Linux Kernel

High severity, CVSS 7.8. EPSS: 0.4% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: usb: cdc-acm: Check control transfer buffer size before access If the first fragment is shorter than struct usb_cdc_notification, we can't calculate an expected_size. Log an error and discard the notification instead of reading lengths from memory outside the received data, which can lead to memory corruption when the expected_size decreases between fragments, causing `expected_size - acm->nb_index` to wrap. This issue has been present since the beginning of git history; however, it only leads to memory corruption since commit ea2583529cd1 ("cdc-acm: reassemble fragmented notifications"). A mitigating factor is that acm_ctrl_irq() can only execute after userspace has opened /dev/ttyACM*; but if ModemManager is running, ModemManager will do that automatically depending on the USB device's vendor/product IDs and its other interfaces.

Affected products

• Linux Linux Kernel: from 2.6.13, before 5.4.291 (fixed in 5.4.291); from 5.5, before 5.10.235 (fixed in 5.10.235); from 5.11, before 5.15.179 (fixed in 5.15.179); from 5.16, before 6.1.129 (fixed in 6.1.129); from 6.2, before 6.6.79 (fixed in 6.6.79); from 6.7, before 6.12.16 (fixed in 6.12.16); …

Published 2025-02-22. Last modified 2026-06-17.