# CVE-2026-11985: Cross-thread FPU register leak on ARM when FPU enabled without register sharing

> An attacker can read sensitive data from floating-point registers of other threads in Zephyr RTOS when FPU is enabled without register sharing.

- **Severity:** Low 3.6 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N`)
- **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:** No
- **Published:** 11 Aug 2026
- **Updated:** 31 Aug 2026
- **Also known as:** GHSA-qxr9-wh3c-hvgv

## What is CVE-2026-11985?

CVE-2026-11985 is a low-severity vulnerability in zephyrproject zephyr, published on 11 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

On the Zephyr ARM port, enabling the hardware FPU (CONFIG_FPU) forces the "Floating point ABI" choice, which defaults to CONFIG_FP_HARDABI. Both FP_HARDABI and FP_SOFTABI permit the compiler to emit hardware FP instructions in any function, even code that never uses floating-point types. However, the callee-saved FP registers (s16-s31 / d8-d15) are only saved and restored across a context switch when CONFIG_FPU_SHARING is enabled (arch/arm/core/cortex_m/swap_helper.S and arch/arm/core/cortex_a_r/swap_helper.S), and prior to this fix selecting an ABI did not enable FPU register sharing, which defaults off.

In a build that enables the FPU with the default ABI but leaves CONFIG_FPU_SHARING disabled, the kernel preserves no callee-saved FP register state across thread switches. The documented precondition for this "unshared" mode — that only a single thread ever executes FP instructions — is silently violated because the compiler may generate FP instructions in every thread.

Under CONFIG_USERSPACE, where threads are mutually isolated, this becomes an information-disclosure boundary crossing: a victim thread can leave secret-derived values in s16-s31, and a co-resident unprivileged thread can read those registers directly (FP register access is not privilege-gated), recovering data left behind by another thread. Without userspace the same defect causes cross-thread FP state corruption (a correctness fault). The leak is bounded to the 16 callee-saved single-precision registers and is opportunistic, so impact is low.

The fix makes FP_HARDABI and FP_SOFTABI select CONFIG_FPU_SHARING and tags every thread with K_FP_REGS at creation, so callee-saved FP state is always preserved across context switches whenever the compiler may emit FP instructions.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-11985?


## How do I fix CVE-2026-11985?

No fix has been published for CVE-2026-11985 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-11985 being exploited?

There is no known exploitation of CVE-2026-11985 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-11985 and fix it if it is affected.

What it is: CVE-2026-11985 is a low-severity vulnerability in zephyrproject zephyr, published on 11 Aug 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-2026-11985 in the wild and no public exploit code.

Affected product: zephyrproject zephyr. 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-2026-11985/ (Markdown: https://insights.sbomify.com/CVE-2026-11985/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-11985
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-11985
- OSV: https://osv.dev/vulnerability/CVE-2026-11985

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-11985/
Summaries are generated and may contain mistakes; the official description above is the record.