# CVE-2024-21378: Microsoft Outlook Remote Code Execution Vulnerability

> Attackers can execute arbitrary code via Microsoft Outlook, requiring users to apply vendor patches immediately.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 13 Feb 2024
- **Updated:** 10 Aug 2026
- **Also known as:** GHSA-qm4q-xhjm-67jr

## What is CVE-2024-21378?

CVE-2024-21378 is a high-severity code injection vulnerability in Microsoft 365 Apps, published on 13 Feb 2024. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Microsoft Outlook Remote Code Execution Vulnerability

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2024-21378?

It affects 4 products.


Products: Microsoft 365 Apps, Microsoft Office, Microsoft Office Long Term Servicing Channel, Microsoft Outlook.

## How do I fix CVE-2024-21378?

No fix has been published for CVE-2024-21378 yet. Limit exposure of the affected software until one is available.

## Is CVE-2024-21378 being exploited?

There is no known exploitation of CVE-2024-21378 in the wild and no public exploit code.

Public exploit code:

- This repository contains an exploit for targeting Microsoft Outlook through Exchange Online, leveraging a vulnerability to execute arbitrary code via COM DLLs. The exploit utilizes a modified version of Ruler to send a malicious form as an email, triggering the execution upon user interaction within the Outlook thick client. (github_poc): https://github.com/d0rb/CVE-2024-21378

## 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-2024-21378 and fix it if it is affected.

What it is: CVE-2024-21378 is a high-severity code injection vulnerability in Microsoft 365 Apps, published on 13 Feb 2024. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2024-21378 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-2024-21378/ (Markdown: https://insights.sbomify.com/CVE-2024-21378/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2024-21378
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2024-21378
- OSV: https://osv.dev/vulnerability/CVE-2024-21378

---
From sbomify Insights: https://insights.sbomify.com/CVE-2024-21378/
Summaries are generated and may contain mistakes; the official description above is the record.