# CVE-2026-100212: Microsoft Office Excel Remote Code Execution Vulnerability

> An attacker can execute arbitrary code remotely by exploiting a use-after-free flaw in Microsoft Office Excel.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 13 Oct 2026
- **Updated:** 29 Oct 2026
- **Also known as:** GHSA-pj29-hgrw-877w

## What is CVE-2026-100212?

CVE-2026-100212 is a high-severity use after free vulnerability in Microsoft 365 Apps, published on 13 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Use after free in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-100212?

It affects 5 products.


Products: Microsoft 365 Apps, Microsoft Microsoft 365, Microsoft Office 2021, Microsoft Office 2024, Microsoft Office Online Server.

## How do I fix CVE-2026-100212?

No fix has been published for CVE-2026-100212 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-100212 being exploited?

There is no known exploitation of CVE-2026-100212 in the wild and no public exploit code.

## Other vulnerabilities in Microsoft 365 Apps

- [CVE-2024-21413](https://insights.sbomify.com/CVE-2024-21413/): Microsoft Outlook Improper Input Validation (critical 9.8, exploited in the wild)
- [CVE-2023-23397](https://insights.sbomify.com/CVE-2023-23397/): Microsoft Office Outlook Privilege Escalation (critical 9.8, exploited in the wild)
- [CVE-2024-38189](https://insights.sbomify.com/CVE-2024-38189/): Microsoft Project Remote Code Execution Vulnerability (high 8.8, exploited in the wild)
- [CVE-2023-35311](https://insights.sbomify.com/CVE-2023-35311/): Microsoft Outlook Security Feature Bypass (high 8.8, exploited in the wild)
- [CVE-2026-21514](https://insights.sbomify.com/CVE-2026-21514/): Microsoft Office Word Reliance on Untrusted Inputs in a Security Decision (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100212 and fix it if it is affected.

What it is: CVE-2026-100212 is a high-severity use after free vulnerability in Microsoft 365 Apps, published on 13 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-100212 in the wild and no public exploit code.

Affected product: Microsoft 365 Apps. 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-2026-100212/ (Markdown: https://insights.sbomify.com/CVE-2026-100212/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100212
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100212
- OSV: https://osv.dev/vulnerability/CVE-2026-100212

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100212/
Summaries are generated and may contain mistakes; the official description above is the record.