JailbreakMe allows iPhone and iPad users to jailbreak their devices. The website exploits a vulnerability in the way Safari handles PDF files. Previously, jailbreaking has required users to connect their device to a computer before they can start to tamper with the set-up of their iPhone or iPad and gain access to the Cydia underground app store. The jailbreak is possible because the default browser used in the iOS operating system uses PDF files specifically its handling of fonts is vulnerable to a vulnerability.”]
Source: https://grahamcluley.com/jailbreakme-security-warning-iphone-ipad-owners/