# CVE-2026-64293: iommufd: Use sizeof(*hdr) instead of sizeof(hdr) in veventq read

> A buffer overflow in the Linux kernel iommufd subsystem allows attackers to write past user buffers on 32-bit systems, potentially leading to code execution or privilege escalation.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-64293, DEBIAN-CVE-2026-64293, GHSA-rq5j-2985-g74r, ROOT-OS-UBUNTU-2204-CVE-2026-64293, UBUNTU-CVE-2026-64293

## What is CVE-2026-64293?

CVE-2026-64293 is a high-severity memory corruption 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:

iommufd: Use sizeof(*hdr) instead of sizeof(hdr) in veventq read

The bound-check in iommufd_veventq_fops_read() for the normal vEVENT
path uses sizeof(hdr) where the surrounding code uses sizeof(*hdr):

	if (!vevent_for_lost_events_header(cur) &&
	    sizeof(hdr) + cur->data_len > count - done) {

hdr is declared as struct iommufd_vevent_header *, so sizeof(hdr)
evaluates to the size of the pointer.  Surrounding code uses
sizeof(*hdr) consistently:

	if (done >= count || sizeof(*hdr) > count - done) {
	...
	if (copy_to_user(buf + done, hdr, sizeof(*hdr))) {
	...
	done += sizeof(*hdr);

struct iommufd_vevent_header is currently 8 bytes (two __u32 fields,
flags and sequence), so on 64-bit (sizeof(void *) == 8) the two
expressions happen to be equal and the check works as intended.

On 32-bit (sizeof(void *) == 4) the check under-counts the header by
4 bytes: a vEVENT whose data_len causes 8 + cur->data_len to exceed
count - done while 4 + cur->data_len does not will pass the check,
then the loop will copy_to_user 8 bytes of header followed by data_len
bytes of payload, writing past the user-supplied buffer.

It is also a latent bug for any future expansion of struct
iommufd_vevent_header beyond sizeof(void *) on 64-bit; the check
should not depend on the type happening to match the host pointer
width.

Use sizeof(*hdr) to match the rest of the function and the actual
amount that will be copied.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-64293?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64293?

Apply the vendor's patch.

## Is CVE-2026-64293 being exploited?

There is no known exploitation of CVE-2026-64293 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-2026-64293 and fix it if it is affected.

What it is: CVE-2026-64293 is a high-severity memory corruption 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-2026-64293 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-2026-64293/ (Markdown: https://insights.sbomify.com/CVE-2026-64293/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64293
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64293
- OSV: https://osv.dev/vulnerability/CVE-2026-64293

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64293/
Summaries are generated and may contain mistakes; the official description above is the record.