To put it in the simplest terms, ‘Jailbreaking’ an iPhone is similar to ‘rooting’ your Android phone, but the motivations and scope of these actions are very different. In both cases, you (somewhat illegitimately) gain complete control over your phones but both actions can also render your phone vulnerable to malicious actions. The act of jailbreaking usually involves exploiting vulnerability — either in the operating system code or within the device hardware — to gain privileges as an administrative account or ‘root’ on the device.
Jailbreaking has several advantages from the end-user perspective:
Third-party apps: Apps that are unavailable through the official App Store can be installed on jailbroken devices. This may include apps that have been banned, removed, deleted, rejected, or generally censored by the official App Store.
Tweaks: Several unofficial tweaks and customizations are made by third-party developers, which can drastically alter the interface of your iPhone.
Unlocking: Carrier-locked and region-locked iPhones can be unlocked and used with other carriers and in other regions.
Privacy: Control the uploading of telemetry and usage statistics to Apple servers.
However, from a security perspective, jailbreaking can introduce some serious vulnerabilities on your iPhone:
Piracy: The most common reason for jailbreaking iPhones is to circumvent the official App Store and install pirated apps.
Malware: Malicious actors often install malware and tracking software on jailbroken devices.
Worm: An insecure SSH service on jailbroken devices can allow an attacker to gain entry onto your device and compromise your device usage.
Since users with jailbroken iPhones are more vulnerable than regular iPhone users and more likely to install pirated apps, it is in Apple’s interest to proactively patch any vulnerabilities that can be used to jailbreak iPhones. Therefore, Apple actively releases various software patches for iOS to close down any and all jail-break vulnerabilities that are found. This is why most jailbreaking software ends up disabling OTA updates to ensure that users don’t accidentally install these patches released by Apple. However, if there happens to be a bootroom exploit, that is, an exploit found in the hardware of the device, it cannot be patched, unless you upgrade to a newer handset
However, if there happens to be a bootroom exploit, that is, an exploit found in the hardware of the device, it cannot be patched, unless you upgrade to a newer handset with newer hardware that does not contain the exploit. For instance, in September 2019, a bootroom exploit called checkm84 was discovered that affected all iPhone models up to and including iPhone X.
Hope this was helpful.