CVE-2026-31721 usb: gadget: f_hid: move list and spinlock inits from bind to alloc
A race condition in the Linux kernel USB HID gadget driver can cause list corruption and system crashes when unbinding and rebinding the UDC while file descriptors are active.
- 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-2026-31721?
CVE-2026-31721 is a medium-severity vulnerability in Linux kernel, published on 1 May 2026. 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: gadget: f_hid: move list and spinlock inits from bind to alloc
There was an issue when you did the following: - setup and bind an hid gadget - open /dev/hidg0 - use the resulting fd in EPOLL_CTL_ADD - unbind the UDC - bind the UDC - use the fd in EPOLL_CTL_DEL
When CONFIG_DEBUG_LIST was enabled, a list_del corruption was reported within remove_wait_queue (via ep_remove_wait_queue). After some debugging I found out that the queues, which f_hid registers via poll_wait were the problem. These were initialized using init_waitqueue_head inside hidg_bind. So effectively, the bind function re-initialized the queues while there were still items in them.
The solution is to move the initialization from hidg_bind to hidg_alloc to extend their lifetimes to the lifetime of the function instance.
Additionally, I found many other possibly problematic init calls in the bind function, which I moved as well.
Which versions are affected by CVE-2026-31721?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31721?
Apply the vendor's patch.
Is CVE-2026-31721 being exploited?
There is no known exploitation of CVE-2026-31721 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31721, DEBIAN-CVE-2026-31721, GHSA-8r63-5629-3mpc, ROOT-OS-DEBIAN-11-CVE-2026-31721, ROOT-OS-UBUNTU-2204-CVE-2026-31721, ROOT-OS-UBUNTU-2404-CVE-2026-31721 and 1 more.