Apple Update Patches Serious iOS 12.4 Jailbreaking Flaw

Apple has patched a serious flaw in iOS 12.4 that allowed for iPhone jailbreaks but also exposed the smartphone to takeovers from a malicious app.

The fix arrives in iOS 12.4.1, which Apple released on Monday. Oddly, Apple originally fixed this bug back in May, but accidentally re-introduced it in iOS 12.4. So far, Apple hasn't commented on why this happened, but the flaw is pretty serious; it can let a malicious app execute computer code on an iPhone with system privileges, bypassing the onboard security safeguards.

A week ago, hacker Pwn20wnd exploited the bug to create a publicly available jailbreaking tool for iPhones and iPads with iOS 12.4 installed. By using the tool, consumers can remove the iOS restrictions and modify the software to install unsanctioned third-party apps.

On the flip side, the same bug can open the door for cybercriminals and state-sponsored hackers to plant malware on iOS devices. This can be done by tricking a victim into installing a rogue app to secretly trigger the flaw, which would pave the way for a remote takeover.

In Apple's release notes for iOS 12.4.1, the company went out of its way to thank Pwn20wnd for the hacker's "assistance" in publicizing the flaw. Pwn20wnd, meanwhile, is telling his Twitter followers to avoid upgrading to the latest version of iOS if they'd like to jailbreak their device. The hacker has a Github page, where you can install the jailbreaking tool "unc0ver." PCMag hasn't tried the tool, but there are various videos tutorials on YouTube with instructions on how to install it.

About Our Expert

Michael Kan

Principal Reporter

My Experience

I've been a journalist for over 15 years. I got my start as a schools and cities reporter in Kansas City and joined PCMag in 2017, where I cover satellite internet services, cybersecurity, PC hardware, and more. I'm currently based in San Francisco, but previously spent over five years in China, covering the country's technology sector.

Since 2020, I've covered the launch and explosive growth of SpaceX's Starlink satellite internet service, writing 600+ stories on availability and feature launches, but also the regulatory battles over the expansion of satellite constellations, fights with rival providers like AST SpaceMobile and Amazon, and the effort to expand into satellite-based mobile service. I've combed through FCC filings for the latest news and driven to remote corners of California to test Starlink's cellular service.

I also cover cyber threats, from ransomware gangs to the emergence of AI-based malware. In 2024 and 2025, the FTC forced Avast to pay consumers $16.5 million for secretly harvesting and selling their personal information to third-party clients, as revealed in my joint investigation with Motherboard.

I also cover the PC graphics card market. Pandemic-era shortages led me to camp out in front of a Best Buy to get an RTX 3000. I'm now following how the AI-driven memory shortage is impacting the entire consumer electronics market. I'm always eager to learn more, so please jump in the comments with feedback and send me tips.

The Best Tech I've Had:

My first video game console: a Nintendo Famicom
I loved my Sega Saturn despite PlayStation's popularity.
The iPod Video I received as a gift in college
Xbox 360 FTW
The Galaxy Nexus was the first smartphone I was proud to own.
The PC desktop I built in 2013, which still works to this day.

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