Anti Rollback Xiaomi: full protection or obstacle to custom firmware?

Owners of Xiaomi, Redmi, and POCO devices interested in flashing or unlocking a bootloader often come across the chilling term “Anti Rollback.” This protection system is built into the device’s software code and is designed to prevent older versions of the operating system from being installed. For the average user updating through OTA, it’s an unobtrusive process, but for Android modification enthusiasts, knowing the mechanisms of ARB becomes a critical survival skill.

The essence of the technology is to compare special version tags when you try to write a new image of the system. If you try to install firmware with a lower security index than the one already recorded in the memory of the chip, the process will be interrupted. At best, the phone will simply refuse to update, at worst, it will go into Hard Brick mode, restored only through service tools like EDL. Understanding how this barrier works will save your gadget from becoming a useless piece of plastic.

In this article, we will discuss in detail why the company has implemented such strict restrictions and whether there are ways to get around them without fatal consequences. You will learn where to look for information about the current status of protection and what actions are strictly prohibited when working with Bootloader. Your data security and smartphone performance directly depend on a competent approach to the issue of rollback versions of software.

The principle of protection against rollback versions

The Anti Rollback (ARB) mechanism is based on a special counter that is stored in a secure area of the processor memory. Every official firmware released by the manufacturer contains a security level label. When you try to reflash the device, the bootloader reads this tag from the firmware file and compares it with the current value of the counter in the phone's memory.

If the new firmware label is higher or equal to the current one, the installation process is successful, and the counter can be upgraded to a new value. However, if you try to install a lower-index image, locking will work, so that malicious users can not exploit vulnerabilities of older versions of Android or MIUI to gain unauthorized access to the system.

It is important to understand the difference between a simple change in the firmware region and a rollback of the version. Switching from global to Chinese (or vice versa) is often possible without changing the ARB index if the version numbers match. But trying to return from MIUI 14 to MIUI 12 on devices with enabled protection is almost guaranteed to lead to a lockdown.

⚠️ Warning: Attempt to force the old firmware through Fastboot mode on devices with active ARB This can lead to permanent locking of the bootloader, and recovery is possible only through an authorized Mi Flash Pro account.

Not only does the system prevent installation, it physically prevents data from being written to certain memory areas if security conditions are not met, which is why you can find messages on forums about a “locked bootloader” after unsuccessful experiments, and the bootloader becomes blocked even if it was previously unlocked by the user.

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Before any firmware manipulation, always check the build number and Anti Rollback index in the About Phone section and on the developers website.

How to check the status of Anti Rollback on your device

Before you start any software action, you need to know the current state of protection. There are several ways to get this information, from simple settings to using console commands. The most reliable method is using ADB (Android Debug Bridge).

First, you need to turn on USB debugging in the developer menu. After connecting your smartphone to your computer, run the command in the terminal:

adb shell getprop ro.boot.avb_version

This command will show the Android Verified Boot (AVB) version of protection that is closely related to the ARB. You can also check the environment variables associated with the base version:

adb shell getprop ro.bootimage.build.date.utc

A more visual way is to use specialized applications from the Google Play store, such as “Device Info HW” or “AIDA64.” In the “System” or “Android” section, look for the Anti-Rollback or ARB field.

• 🔍 Through Fastboot: Put your phone in fast boot mode and connect to your PC. Enter fastboot getvar all. anti_version. The number next to it will indicate the level.
• 📱 About Phone: Sometimes (rarely) information is contained in the details of the kernel version, but most often this data is hidden from the average user.
• 💻 Software for firmware: Utilities like Xiaomi ADB/Fastboot Tools often automatically read and display protection status when connecting a device.

If the ARB is 0, then the protection on your device is not activated or implemented by the manufacturer for this model, this is typical for older models or some budget lines. A value of 1 or higher indicates that the mechanism works, and you can not roll back below this version.

Consequences of an attempted firmware rollback

What happens if you ignore the warnings and try to install the old version of the software? There can be several scenarios, and they all depend on the model of the processor and the specific implementation of protection in MIUI. In the most “soft” case, the firmware process will simply be interrupted with an error in the console.

But most of the time, the device goes into a state known as Soft Brick. The phone stops booting, the screen goes out or freezes on the logo, and cyclic reboot becomes the norm. In this mode, sometimes logging into Recovery and resetting to factory settings helps, but if the bootloader is damaged, it won't save you.

The most critical scenario is Hard Brick, which completely stops responding to buttons, the screen is black, the computer does not emit a USB connection sound, although the consumption current can increase, in which case only EDL (Emergency Download Mode) mode helps, which often requires disassembling the smartphone and closing contacts on the board to enter.

⚠️ Warning: Some Qualcomm models have fuse protection, which is the physical burning of microscopic jumpers inside the chip, and it's technically impossible to reverse this process without replacing the motherboard.

Can you get around Anti Rollback?

The issue of circumvention is a concern for many, especially those who want to install custom firmware on older Android, and the short answer is that it's almost impossible to get around it, and the only way to get around it is by having access to the manufacturer's private signature keys, which are, of course, not available to the public.

There are methods of modifying boot images, where enthusiasts try to “swap” the version label in the firmware files. However, modern AVB 2.0 integrity verification algorithms will immediately detect a digital signature discrepancy, the system will recognize that the image has been changed, and refuse to run it.

The only workable but difficult way is to find specific models that allow you to skip the checkout, exploits that are usually quickly closed with a security update, and use such methods requires a deep knowledge of Linux and the structure of Android.

• 🚫 Modification of Fastboot: Attempts to change the executable file of the Fastboot utility on the PC will not give results, since the verification takes place on the device side.
• 🔓 Unlocked bootloader: Having an unlocked Bootloader does not cancel the action ARB. You can put custom recavers, but the old official firmware still will not stand up.
• 🛠 Test Point: Using test points to enter EDL sometimes allows you to flash the device bypassing some checks, but does not always bypass the meter itself ARB.

If you want to get super-user rights or install Google Camera, you don't need to bypass ARBs, but these are done on current versions of the software. The desire to roll back is usually dictated by the desire to return old features or performance, which on modern hardware is often meaningless.

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Anti Rollback circumvention is only theoretically possible through vulnerabilities that are quickly fixed. It's almost safer to accept the constraint.

Instructions for safe flashing

To minimize the risks and avoid being blocked, follow a strict algorithm of actions, the main rule: never flash your device with files that you do not know the purpose of, or files for other models.

Before starting the procedure, make sure to make a full backup of the data. Even a successful firmware can require a complete reset (Wipe Data), which will delete all photos, contacts and applications.

Use only the original tools. For Windows, this is Mi Flash Tool. When you select firmware mode in the utility, look carefully at the options available. clean_all It's safe, but here it is. clean_all_and_lock locks the bootloader back, which can be problematic if you plan on further modifications.

The firmware process is as follows:

1. Unpack the firmware archive in the root of the C disk (the path should not contain Cyrillic).
2. Run Mi Flash on behalf of the administrator.
3. Press the Refresh button and make sure the device is identified.
4. At the bottom, select Save User Data (if you don’t need a reset) or Clean All.
5. Press Flash and wait for the end. Don't touch the cable!

⚠️ Warning: Never interrupt the firmware process, even if it seems to be frozen. Interrupting the write to the system partition is guaranteed to cause the phone to fail.

Frequently Asked Questions (FAQ)