Before i proceed i will like to give credits to hASOON2000 and djrbliss of xda developers forum for this root guide.
This root guide4 is code named X-Factor root exploit.
For root to be attained on a device, rooted users simply have to wait for ROM devs to get the stock, rooted ROM up and then flash to it. However, sometimes it isn’t that easy most especially for people who bought the phone after the firmware update.
What made the rooting of HTC AT& T so challenging was, of course, HTC. In earlier firmware versions, users could unlock their bootloaders using HTCDev. With the latest 2.20 update, the bootloader was locked down and remained that way. That is, until XDA Forum Member djrbliss released a root method that was able to get past that. Essentially, the method involves using an exploit to overwrite the CID so that HTCDev’s website will recognize it and unlock the bootloader.
PROCESS OF ROOTING THE HTC AT & T ON FIRMWARE BUILD 2.20:
It’s impossible to have a “permanent root” on 2.20 in the traditional sense without unlocking the bootloader.
This tutorial contains an an exploit that gains temporary root access by leveraging two vulnerabilities and uses these newly gained root privileges to overwrite the CID (“superCID”), so that it’s possible to unlock the bootloader via HTC’s website. I’m sorry if you’d prefer to not unlock your bootloader this way, but there are no other options for root access available.
WARNING & DISCLAIMER:
As we all know that anything can happen in the technological world so i always advice people to backup the phones before performing any rooting or firmware update you can do this by using titanum backup, external harddisk, external sdcard and ES File Explorer.
>>. This exploit modifies the CID of your device. Doing so likely voids your warranty, and may be in violation of your contract with AT&T . Additionally, while this exploit has been tested and has not been observed to cause any negative side effects in practice, I am not to be held responsible if you damage your device in the process.
and for LINUX/ MAC COMPUTERS: http://vulnfactory.org/public/X_Factor_Linux_OSX.zip
NOW THE PROCESS:
>>. Extract the entire zip file.
>>. Connect your device via USB, ensure you have the latest HTC USB drivers installed (only on Windows), and ensure USB debugging mode is enabled.
>>. Double-click “run.bat”, or if running Linux or OSX, open a terminal, change directories to the extracted exploit, and run “./run.sh”.
>>. Follow the instructions printed by the exploit. You will need to authorize two backup restorations during the exploit’s execution.
>>. If the exploit is successful, it will print “[+] Set CID!”. If it does not print this, the exploit has failed, so please do not continue.
>>. The exploit will automatically reboot into bootloader mode. Press enter after bootloader mode is finished booting, and the exploit will print your CID. If the exploit was successful, it should return “11111111” as your CID.
>>. If your CID was successfully set, press enter to generate an unlock token.
>>. Visit htcdev.com, navigate to the “Bootloader unlock” section, choose “All other supported models” from the drop-down menu, and provide the unlock token when asked.
>>After unlocking the bootloader, you can flash a custom recovery partition via fastboot, boot into recovery mode, and use a recovery ADB shell or install from an update.zip to install Superuser and su
NOTE: IF BY ANY MEANS YOU THINK THIS PROCESS IS COMPLEX THEN YOU MAY TRY THE ALTERNATIVE METHOD WHICH WAS POSTED BY hasoon2000 of XDA Dev HERE