# CVE-2021-36934: Microsoft Windows SAM Local Privilege Escalation

> Attackers with local access can escalate privileges to SYSTEM via permissive ACLs on system files, requiring manual shadow copy deletion after patching.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:T/RC:C`)
- **Exploited in the wild:** Yes, since 10 Feb 2022 (CISA KEV)
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Jul 2021
- **Updated:** 10 Aug 2026
- **Also known as:** GHSA-x4m2-px5g-5q55

## What is CVE-2021-36934?

CVE-2021-36934 is a high-severity vulnerability in Microsoft Windows 10 1809, published on 22 Jul 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

An elevation of privilege vulnerability exists because of overly permissive Access Control Lists (ACLs) on multiple system files, including the Security Accounts Manager (SAM) database. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights.
An attacker must have the ability to execute code on a victim system to exploit this vulnerability.
After installing this security update, you must manually delete all shadow copies of system files, including the SAM database, to fully mitigate this vulnerabilty. Simply installing this security update will not fully mitigate this vulnerability. See KB5005357- Delete Volume Shadow Copies.

## Which versions are affected by CVE-2021-36934?

It affects 5 products.


Products: Microsoft Windows 10 1809, Microsoft Windows 10 1909, Microsoft Windows 10 2004, Microsoft Windows 10 20h2, Microsoft Windows 10 21h1.

## How do I fix CVE-2021-36934?

No fix has been published for CVE-2021-36934 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 24 Feb 2022.

## Is CVE-2021-36934 being exploited?

Yes. Attackers have exploited CVE-2021-36934 in the wild since at least 10 Feb 2022.

Public exploit code:

- Pure Nim implementation for exploiting CVE-2021-36934, the SeriousSAM local privilege escalation (github_poc): https://github.com/HuskyHacks/ShadowSteal
- PoC for CVE-2021-36934, which enables a standard user to be able to retrieve the SAM, Security, and Software Registry hives in Windows 10 version 1809 or newer (github_poc): https://github.com/WiredPulse/Invoke-HiveNightmare
- Fix for the CVE-2021-36934 (github_poc): https://github.com/JoranSlingerland/CVE-2021-36934
- HiveNightmare a.k.a. SeriousSam Local Privilege Escalation in Windows – CVE-2021-36934 (github_poc): https://github.com/romarroca/SeriousSam
- Small and dirty PoC for CVE-2021-36934 (github_poc): https://github.com/Wh04m1001/VSSCopy
- PoC for CVE-2021-36934 Aka HiveNightmare/SeriousSAM written in python3 (github_poc): https://github.com/Sp00kySkelet0n/PyNightmare

## Other vulnerabilities in Microsoft Windows 10 1809

- [CVE-2024-29988](https://insights.sbomify.com/CVE-2024-29988/): Microsoft SmartScreen Prompt Security Feature Bypass (high 8.8, exploited in the wild)
- [CVE-2024-21412](https://insights.sbomify.com/CVE-2024-21412/): Microsoft Windows Internet Shortcut Files Security Feature Bypass (high 8.1, exploited in the wild)
- [CVE-2025-62221](https://insights.sbomify.com/CVE-2025-62221/): Microsoft Windows Use After Free (high 7.8, exploited in the wild)
- [CVE-2025-30400](https://insights.sbomify.com/CVE-2025-30400/): Microsoft Windows DWM Core Library Use-After-Free (high 7.8, exploited in the wild)
- [CVE-2024-21338](https://insights.sbomify.com/CVE-2024-21338/): Microsoft Windows Kernel Exposed IOCTL with Insufficient Access Control (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36934 and fix it if it is affected.

What it is: CVE-2021-36934 is a high-severity vulnerability in Microsoft Windows 10 1809, published on 22 Jul 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: Yes. Attackers have exploited CVE-2021-36934 in the wild since at least 10 Feb 2022.

Affected product: Microsoft Windows 10 1809. 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-2021-36934/ (Markdown: https://insights.sbomify.com/CVE-2021-36934/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36934
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36934
- OSV: https://osv.dev/vulnerability/CVE-2021-36934

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36934/
Summaries are generated and may contain mistakes; the official description above is the record.