# CVE-2026-6687: FatFs Stack Buffer Overflow via Uncapped exFAT Label Length

> Attackers can trigger a stack buffer overflow in FatFs by providing a malicious exFAT label, potentially leading to code execution or system crashes.

- **Severity:** High 7.6 (`CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 1 Jul 2026
- **Updated:** 1 Jul 2026
- **Also known as:** GHSA-wghw-hg6m-7rh3

## What is CVE-2026-6687?

CVE-2026-6687 is a high-severity memory corruption vulnerability in ChaN FatFs, published on 1 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

FatFs R0.16 and earlier contains a stack overflow bug in f_getlabel() because exFAT label length (XDIR_NumLabel) is trusted without enforcing spec maximums. This maps to CWE-121 (Stack-based Buffer Overflow). Estimated CVSS v3.1 vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H (7.6, High). The estimated CISA SSVC vectors are Exploitation: PoC, Technical Impact: Total.

Weakness: CWE-121 (Stack-based Buffer Overflow)

## Which versions are affected by CVE-2026-6687?

It affects 1 product.


Products: Elm-Chan Fatfs.

## How do I fix CVE-2026-6687?

No fix has been published for CVE-2026-6687 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6687 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6687 exists.

## Other vulnerabilities in ChaN FatFs

- [CVE-2026-6682](https://insights.sbomify.com/CVE-2026-6682/): FatFs Integer Overflow in FAT32 Volume Mount (high 7.6)
- [CVE-2026-6688](https://insights.sbomify.com/CVE-2026-6688/): FatFs Buffer Overflow via Unbounded LFN Filename Copy (high 7.6)
- [CVE-2026-6683](https://insights.sbomify.com/CVE-2026-6683/): FatFs Divide-by-Zero in exFAT Sync (medium 4.6)
- [CVE-2026-6684](https://insights.sbomify.com/CVE-2026-6684/): FatFs Infinite Loop in GPT Partition Scan (medium 4.6)
- [CVE-2026-6686](https://insights.sbomify.com/CVE-2026-6686/): FatFs Use of Uninitialized Clusters After Seek Past EOF (medium 4.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6687 and fix it if it is affected.

What it is: CVE-2026-6687 is a high-severity memory corruption vulnerability in ChaN FatFs, published on 1 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-6687 exists.

Affected product: ChaN FatFs. 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-2026-6687/ (Markdown: https://insights.sbomify.com/CVE-2026-6687/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6687
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6687
- OSV: https://osv.dev/vulnerability/CVE-2026-6687

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6687/
Summaries are generated and may contain mistakes; the official description above is the record.