CVE-2026-80854 usb: gadget: f_tcm: keep port count until LUN teardown completes
A race condition in the Linux kernel USB gadget driver allows a use-after-free, potentially causing a system crash or arbitrary code execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-80854?
CVE-2026-80854 is an use after free vulnerability in Linux, published on 4 Sep 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_tcm: keep port count until LUN teardown completes
tcm_usbg_drop_nexus() permits session removal once tpg_port_count reaches zero. However, usbg_port_unlink() currently decrements that count from the fabric_pre_unlink() callback, before core_dev_del_lun() waits for active se_lun references to drain.
If removal of the last LUN races a nexus removal, the latter can observe a zero port count and call target_remove_session(). This frees sess_cmd_map while an in-flight struct usbg_cmd, including its work item, can still be accessed.
Overlapping the last-LUN unlink with nexus removal reproduces this lifetime violation as a DEBUG_OBJECTS "free active" warning for usbg_cmd_work, followed by a target-core BUG/Oops.
The generic target-core unlink path has no callback after core_dev_del_lun() completes. Add an optional fabric_post_unlink() callback and use it for the f_tcm port count. The count now remains nonzero until core_dev_del_lun() has finished draining active LUN references, preventing nexus removal from freeing the session during command completion.
Which versions are affected by CVE-2026-80854?
How do I fix CVE-2026-80854?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-80854 being exploited?
There is no known exploitation of CVE-2026-80854 in the wild and no public exploit code.
Sources
Also known as AZL-99537, BELL-CVE-2026-80854, DEBIAN-CVE-2026-80854, GHSA-g824-q393-34qq, UBUNTU-CVE-2026-80854.