mirror of
https://github.com/anotherhadi/blog.git
synced 2026-08-23 04:55:50 +02:00
Hadi
68 lines
1.5 KiB
Markdown
68 lines
1.5 KiB
Markdown
---
|
|
title: "GRUB Boot Bypass"
|
|
description: "Physical access techniques to get a root shell by editing GRUB boot parameters."
|
|
tags: ["linux", "grub", "physical-access", "privesc"]
|
|
publishDate: 2026-05-18
|
|
---
|
|
|
|
When GRUB is not password-protected, anyone with physical access can edit boot parameters and bypass authentication entirely.
|
|
|
|
At the GRUB menu, press **`e`** to edit the selected entry. Modify the line starting with `linux`, then press **`F10`** to boot.
|
|
|
|
## Techniques
|
|
|
|
### init=/bin/sh
|
|
|
|
Replaces the init process with a shell; drops directly into a root shell before any login prompt.
|
|
|
|
```
|
|
linux ... init=/bin/sh
|
|
```
|
|
|
|
Filesystem is mounted read-only by default. Remount to make changes:
|
|
|
|
```bash
|
|
mount -o remount,rw /
|
|
```
|
|
|
|
### init=/bin/bash
|
|
|
|
Same as above but uses bash. Add `rw` on the `linux` line to mount read-write from the start:
|
|
|
|
```
|
|
linux ... rw init=/bin/bash
|
|
```
|
|
|
|
### rd.break (systemd)
|
|
|
|
Interrupts the boot process in the initramfs, before the real root filesystem is mounted. Useful for resetting the root password.
|
|
|
|
```
|
|
linux ... rd.break
|
|
```
|
|
|
|
From the initramfs shell:
|
|
|
|
```bash
|
|
mount -o remount,rw /sysroot
|
|
chroot /sysroot
|
|
passwd root
|
|
exit
|
|
```
|
|
|
|
### single (single-user mode)
|
|
|
|
Boots into maintenance mode. On some distros this drops to a root shell without a password prompt (not Debian/Ubuntu).
|
|
|
|
```
|
|
linux ... single
|
|
```
|
|
|
|
### systemd.unit=rescue.target
|
|
|
|
systemd equivalent of single-user mode: minimal services, root shell.
|
|
|
|
```
|
|
linux ... systemd.unit=rescue.target
|
|
```
|