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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
HIGH 7.8
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-19
Original CVE updated
2026-07-27
Advisory published
2026-07-19
Advisory updated
2026-07-27

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.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-63894 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-63894

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-63894 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-63894

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/2796646f6d892c1eb6818c7ca41fdfa12568e8d1

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/552dae28dbeb5f7c4fafcda43962dc46569f58a0

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/c7d421123b98d5e9c1c84bd9957aba36f1cbb4ca

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

  • Source reference

    Unverified legacy reference

    URL: https://git.kernel.org/stable/c/c872d8a065b3b499ce4c3ad168b5d34b68524f66

    416baaa9-dc9f-4396-8d5f-8c081fb06d67

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.