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PatchSiren cyber security CVE debrief

CVE-2026-63894 Linux CVE debrief

The Linux kernel was vulnerable to a use-after-free issue in the FunctionFS (f_fs) USB gadget driver, specifically in the DMABUF handling code. When a DMABUF was detached or the file was released, the code failed to properly synchronize the cancellation of DMABUF requests with their completion, leading to a potential use-after-free error. An attacker with control over the FunctionFS device node, typically owned by a privileged gadget daemon, could potentially exploit this vulnerability to access freed memory.

Vendor
Linux
Product
Unknown
CVSS
Unknown
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-19
Original CVE updated
2026-07-19
Advisory published
2026-07-19
Advisory updated
2026-07-19

Who should care

System administrators and developers using the Linux kernel with USB gadget functionality, especially those with privileged access to the FunctionFS device node, should be aware of this vulnerability and apply the provided patch to prevent potential exploitation.

Technical summary

The vulnerability was caused by the lack of proper synchronization between the cancellation of DMABUF requests and their completion in the f_fs USB gadget driver. The patch moves the freeing of the usb_request into the ffs_dmabuf_cleanup() work handler, which runs under the eps_lock, ensuring that the request is not freed prematurely. This change prevents the use-after-free error and ensures the stability of the Linux kernel's USB gadget functionality.

Defensive priority

High

Recommended defensive actions

  • Apply the provided patch to the Linux kernel to fix the use-after-free vulnerability in the f_fs USB gadget driver.
  • Ensure that the Linux kernel is updated with the latest security patches.
  • Monitor system logs for any suspicious activity related to the USB gadget functionality.
  • Review compensating controls for exposed systems while remediation is scheduled and verified.
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review.
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented.
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.

Evidence notes

The vulnerability was discovered and resolved by the Linux kernel developers. The patch was backported to stable kernel versions. The NVD entry for this CVE provides additional information on the vulnerability.

Official resources

AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-19T16:17:06.850Z and has not been modified since then.