---
title: "HOST-USR-004 Duplicate User IDs"
canonical: https://openvapt.com/checks/HOST-USR-004.html
html: https://openvapt.com/checks/HOST-USR-004.html
site: OpenVAPT, https://openvapt.com/
license: OpenVAPT Source-Available Licence 1.3, https://openvapt.com/legal/licence-text.html
modified: 2026-10-14
version: 0.1.0-alpha.6
---

# HOST-USR-004 Duplicate User IDs

Checks that no two accounts share the same numeric user id.

- Domain: Server
- Severity: Medium
- Control category: Identity and Authentication
- Fix effort: medium
- CVSS v3.1 vector: `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N`
- CIS Controls v8: 5.2
- NIST CSF 2.0: PR.AA-01
- CWE: CWE-286
- NIST SP 800-53 Rev. 5: AC-2, IA-2
- Benchmark topic: No duplicate UIDs (topic only, no benchmark text)

## Why It Matters

Accounts with the same UID are the same user to the kernel: they own each other's files and processes, and audit logs cannot tell them apart.

## How It Detects

Reads /etc/passwd and reports any UID used by more than one account.

## How to Fix

Give each account a unique UID (usermod -u <new-uid> <user>) and fix file ownership (find / -xdev -uid <old-uid>).

## How to Verify

```
cut -d: -f3 /etc/passwd | sort | uniq -d  should print nothing.
```

## Learn the Theory

- [P7 Identity, Passwords and Privilege](https://openvapt.com/academy/p7.md)
- [P15 Access Control: Accounts, Sudo and Logins](https://openvapt.com/academy/p15.md)

## References

- [passwd(5), Linux man-pages](https://man7.org/linux/man-pages/man5/passwd.5.html)

## Source Code

https://github.com/OpenVAPT/openvapt/blob/574f7f3333c44b75a3c649e2d93a76d507f75adf/internal/checks/host/passwords.go

Run it: `openvapt scan --only HOST-USR-004`. Read it offline: `openvapt explain HOST-USR-004`.

---

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