CVE-2025-21704 usb: cdc-acm: Check control transfer buffer size before access
A memory corruption vulnerability in the Linux kernel's cdc-acm driver allows attackers to potentially execute code or escalate privileges via crafted USB notifications.
- 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
What is CVE-2025-21704?
CVE-2025-21704 is a high-severity memory corruption vulnerability in Linux kernel, published on 22 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: 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.
Weakness: CWE-787
Which versions are affected by CVE-2025-21704?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21704?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2025-21704 being exploited?
There is no known exploitation of CVE-2025-21704 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21704, DEBIAN-CVE-2025-21704, GHSA-48g3-w2gf-xjrv, ROOT-OS-UBUNTU-2404-CVE-2025-21704, UBUNTU-CVE-2025-21704.