Nefarious actors could use the vulnerability to circumvent Apple’s iCloud account locks, which are used to render stolen or lost devices useless, or to install poisoned versions of iOS that steal user information.
https://www.theverge.com/2019/9/27/20886835/iphone-exploit-checkm8-axi0mx-security-flaw-vunerability-jailbreak-permanent-bootrom-ios
https://www.theverge.com/2019/9/27/20886835/iphone-exploit-checkm8-axi0mx-security-flaw-vunerability-jailbreak-permanent-bootrom-ios