# CVE-2026-98764: usb: gadget: f_fs: Fix NULL pointer dereference in FUNCTIONFS_ENDPOINT_DESC

> A local attacker with access to FunctionFS can trigger a kernel NULL pointer dereference and system crash by querying endpoint descriptors when only full-speed descriptors are provided.

- **Severity:** Not scored
- **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:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-108765, BELL-CVE-2026-98764, DEBIAN-CVE-2026-98764, GHSA-2g29-xq2m-qcrf, UBUNTU-CVE-2026-98764

## What is CVE-2026-98764?

CVE-2026-98764 is a vulnerability in Linux, published on 18 Oct 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_fs: Fix NULL pointer dereference in FUNCTIONFS_ENDPOINT_DESC

When user space sets up FunctionFS with only full-speed descriptors
(e.g., flags = FUNCTIONFS_HAS_FS_DESC) and the gadget operates at a
higher speed (such as USB_SPEED_HIGH or USB_SPEED_SUPER),
config_ep_by_speed() detects that the function lacks descriptors for
the current speed, logs a warning, and falls back to full-speed
descriptors. The endpoint is then successfully enabled via
usb_ep_enable(), and epfile->ep becomes valid.

However, when user space subsequently issues the FUNCTIONFS_ENDPOINT_DESC
ioctl to query the endpoint descriptor, ffs_epfile_ioctl() selects the
descriptor index solely based on gadget->speed:

	switch (epfile->ffs->gadget->speed) {
	case USB_SPEED_SUPER:
	case USB_SPEED_SUPER_PLUS:
		desc_idx = 2;
		break;
	case USB_SPEED_HIGH:
		desc_idx = 1;
		break;
	default:
		desc_idx = 0;
	}
	desc = epfile->ep->descs[desc_idx];
	memcpy(&desc1, desc, desc->bLength);

Because user space only supplied full-speed descriptors,
epfile->ep->descs[1] is NULL. Dereferencing desc->bLength triggers an
immediate kernel NULL pointer dereference panic.

Fix this by falling back through lower speed descriptors if the current
speed descriptor was not supplied, matching the fallback logic in
config_ep_by_speed() and historical f_fs behavior. If still missing,
fall back to epfile->ep->ep->desc (the active descriptor), and return
-EINVAL safely if no valid descriptor is found. In addition, mark desc
as const to match struct usb_ep::desc and avoid discarding qualifiers.

## Which versions are affected by CVE-2026-98764?


## How do I fix CVE-2026-98764?

Apply the vendor's patch.

## Is CVE-2026-98764 being exploited?

There is no known exploitation of CVE-2026-98764 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98764 and fix it if it is affected.

What it is: CVE-2026-98764 is a vulnerability in Linux, published on 18 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98764 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98764/ (Markdown: https://insights.sbomify.com/CVE-2026-98764/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98764
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98764
- OSV: https://osv.dev/vulnerability/CVE-2026-98764

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98764/
Summaries are generated and may contain mistakes; the official description above is the record.