Download iOS 11.3.1 (15E302) for iPhone 6s

You will have to note that you can only restore signed IPSW firmware files using iTunes or 3utools.

❌ This IPSW firmware is not being Signed by Apple

Firmware Identifier iPhone8,1
iOS Version 11.3.1
Release Date 2018-04-24
Update Date 2018-04-14
Sha1sum
dae0911e040a9717233e4c751939985ede6c7bf8
Sha256sum
025955983f7fdbf2cc4f3207c4c2d1e25f872cc085763d47f5f50e3792c5bd34
md5sum
8044953b5614a5c52f8ec80ad5e1676e
Size 2.58 GB
FileName
iPhone_4.7_11.3.1_15E302_Restore.ipsw
Status

Download IPSW (2.58GB) Check device info
Release Notes

It should be noted that these are the official release notes for the from Apple

iOS 11.3.1 improves the security of your iPhone or iPad and addresses an issue where touch input was unresponsive on some iPhone 8 devices because they were serviced with non-genuine replacement displays.

Note: Non-genuine replacement displays may have compromised visual quality and may fail to work correctly. Apple-certified screen repairs are performed by trusted experts who use genuine Apple parts. See support.apple.com for more information.

For information on the security content of Apple software updates, please visit this website:

https://support.apple.com/kb/HT201222