# CVE-2026-93266: arm64: RSI: fix field-spanning write warning in attestation token init

> A field-spanning write in the Linux kernel arm64 RSI attestation token initialization can trigger a FORTIFY warning and potential kernel panic.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-93266, DEBIAN-CVE-2026-93266, GHSA-xvwh-h3f9-mq6w, UBUNTU-CVE-2026-93266

## What is CVE-2026-93266?

CVE-2026-93266 is a memory corruption vulnerability in Linux, published on 24 Sep 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:

arm64: RSI: fix field-spanning write warning in attestation token init

The challenge is passed in registers a1 through a8. However, copying to
&regs.a1 makes FORTIFY treat the destination as the single a1 field,
resulting in a field-spanning write warning. [1]

Overlay the SMCCC register structure with an RSI-specific argument
layout and copy the challenge into an explicit 64-byte array. This keeps
the existing a1-a8 argument encoding while giving the copy a correctly
sized destination object.

[1]
memcpy: detected field-spanning write (size 64) of single field "&regs.a1" at ./arch/arm64/include/asm/rsi_cmds.h:119 (size 8)
WARNING: ./arch/arm64/include/asm/rsi_cmds.h:119 at rsi_attestation_token_init+0xdc/0xf8 [arm_cca_guest], CPU#0: cat/3314

## Which versions are affected by CVE-2026-93266?


## How do I fix CVE-2026-93266?

Apply the vendor's patch.

## Is CVE-2026-93266 being exploited?

There is no known exploitation of CVE-2026-93266 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-93266 and fix it if it is affected.

What it is: CVE-2026-93266 is a memory corruption vulnerability in Linux, published on 24 Sep 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-2026-93266 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-2026-93266/ (Markdown: https://insights.sbomify.com/CVE-2026-93266/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-93266
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-93266
- OSV: https://osv.dev/vulnerability/CVE-2026-93266

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-93266/
Summaries are generated and may contain mistakes; the official description above is the record.