# CVE-2026-64339: usb: misc: usbio: bound bulk IN response length to the received transfer

> A malicious USB device can trigger an out-of-bounds read in the Linux kernel usbio driver, leaking adjacent slab memory to user space.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H`)
- **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:** 25 Jul 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64339, DEBIAN-CVE-2026-64339, GHSA-m28f-fmgf-v7cw, ROOT-OS-UBUNTU-2204-CVE-2026-64339, UBUNTU-CVE-2026-64339

## What is CVE-2026-64339?

CVE-2026-64339 is a high-severity vulnerability in Linux kernel, published on 25 Jul 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: misc: usbio: bound bulk IN response length to the received transfer

usbio_bulk_msg() copies bpkt_len = le16_to_cpu(bpkt->len) bytes out of
the bulk IN buffer (usbio->rxbuf, allocated with size usbio->rxbuf_len)
into the caller's buffer.  bpkt_len is fully controlled by the device
and is only checked against ibuf_len; ibuf_len in turn is checked
against usbio->txbuf_len, not against rxbuf_len:

	if ((obuf_len > (usbio->txbuf_len - sizeof(*bpkt))) ||
	    (ibuf_len > (usbio->txbuf_len - sizeof(*bpkt))))
		return -EMSGSIZE;

txbuf_len and rxbuf_len are taken independently from the bulk OUT and
bulk IN endpoint wMaxPacketSize in usbio_probe().  A malicious or
malfunctioning device that advertises a large bulk OUT endpoint and a
small bulk IN endpoint (e.g. by claiming one of the quirk-free IDs such
as the Lattice NX33U, 0x2ac1:0x20cb) therefore makes ibuf_len, and
hence the device-supplied bpkt_len, exceed rxbuf_len.  memcpy() then
reads up to txbuf_len - rxbuf_len bytes past the end of the rxbuf slab
object.  The over-read bytes are handed back to the i2c layer and on to
user space through i2c-dev, disclosing adjacent slab memory; with KASAN
this is reported as a slab-out-of-bounds read.

The number of bytes actually received is already known: act equals the
URB actual_length and is bounded by rxbuf_len.  Reject any response
that claims more payload than was received, mirroring the existing
"act < sizeof(*bpkt)" check just above.

The control path (usbio_ctrl_msg()) is not affected: it uses a single
buffer (ctrlbuf) for both directions, so its analogous copy can never
leave the allocation.

Found by code review.  The out-of-bounds read was confirmed under
AddressSanitizer with a faithful userspace model of usbio_bulk_msg()'s
receive path (an rxbuf_len-sized buffer, the same act/ibuf_len/bpkt_len
checks and the memcpy).  A USB raw-gadget + dummy_hcd reproducer is
also available.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-64339?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64339?

Apply the vendor's patch.

## Is CVE-2026-64339 being exploited?

There is no known exploitation of CVE-2026-64339 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-64339 and fix it if it is affected.

What it is: CVE-2026-64339 is a high-severity vulnerability in Linux kernel, published on 25 Jul 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-2026-64339 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-64339/ (Markdown: https://insights.sbomify.com/CVE-2026-64339/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64339
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64339
- OSV: https://osv.dev/vulnerability/CVE-2026-64339

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64339/
Summaries are generated and may contain mistakes; the official description above is the record.