# CVE-2026-64402: coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()

> An out-of-bounds write in the Linux kernel's Coresight SMB driver allows attackers to potentially execute code or escalate privileges when using the SMB sink as a perf AUX sink.

- **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:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-64402, DEBIAN-CVE-2026-64402, GHSA-c5fx-2729-67qq, ROOT-OS-UBUNTU-2204-CVE-2026-64402, UBUNTU-CVE-2026-64402

## What is CVE-2026-64402?

CVE-2026-64402 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:

coresight: ultrasoc-smb: Fix OOB write in smb_sync_perf_buffer()

When the SMB sink is used as a perf AUX sink, smb_update_buffer() calls
smb_sync_perf_buffer() to copy hardware trace data into the perf AUX ring
buffer pages. It derives pg_idx = head >> PAGE_SHIFT from @head, which is
handle->head, and indexes dst_pages[pg_idx]. The pg_idx %= nr_pages
normalization is only applied after the first loop iteration.

This leaves the initial page index underived from the buffer size, which
can result in an out-of-bounds write past dst_pages[] when head exceeds
the AUX buffer size.

Normalize head modulo the AUX buffer size before deriving the page index
and offset, mirroring tmc_etr_sync_perf_buffer().

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

## Which versions are affected by CVE-2026-64402?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-64402?

Apply the vendor's patch.

## Is CVE-2026-64402 being exploited?

There is no known exploitation of CVE-2026-64402 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-2026-64402 and fix it if it is affected.

What it is: CVE-2026-64402 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-2026-64402 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-2026-64402/ (Markdown: https://insights.sbomify.com/CVE-2026-64402/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-64402
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-64402
- OSV: https://osv.dev/vulnerability/CVE-2026-64402

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-64402/
Summaries are generated and may contain mistakes; the official description above is the record.