CVE-2021-30807

What is IOMobileFrameBuffer?

IOMobileFrameBuffer is a kernel extension (kext) in iOS, iPadOS, macOS, and watchOS responsible for managing the display frame buffer — the region of memory that stores the image currently displayed on screen. As a kernel-mode component, IOMobileFrameBuffer runs with the highest privilege level on Apple platforms. Memory corruption vulnerabilities in kernel extensions like IOMobileFrameBuffer are among the most severe iOS security bugs because they break out of the iOS app sandbox and achieve kernel code execution — bypassing all application-level security boundaries, SEP (Secure Enclave Processor), and allowing full device control. IOMobileFrameBuffer has been a recurring target for iOS exploit chains, including multiple vulnerabilities in 2021 alone.

Overview

CVE-2021-30807 is an out-of-bounds write vulnerability (CWE-787) in the IOMobileFrameBuffer kernel extension, affecting iOS, iPadOS, macOS Big Sur, and watchOS. A malicious application running on the device can exploit this memory corruption to execute arbitrary code with kernel privileges — breaking the iOS sandbox and achieving full device control. Apple released emergency out-of-band patches on July 26, 2021 (iOS 14.7.1, macOS 11.5.1, watchOS 7.6.1), acknowledging that the vulnerability "may have been actively exploited." CISA added it to KEV in November 2021.

The local attack vector (AV:L) reflects the requirement for a malicious application to be running on the device — typically delivered via a second-stage exploit chain following an initial renderer or WebKit vulnerability, or via a malicious App Store/sideloaded application.

Affected Versions

Technical Details

• Root cause: Out-of-bounds write (CWE-787) in the IOMobileFrameBuffer kernel extension — a memory corruption bug in the kernel component responsible for display frame buffer management
• Kernel code execution: Exploiting the OOB write achieves arbitrary code execution in kernel context — the highest privilege level on iOS/macOS, bypassing the iOS app sandbox, SELinux-equivalent protections, and all user-space security boundaries
• Attack path: A malicious app (AV:L, PR:N) running in the iOS app sandbox triggers the IOMobileFrameBuffer vulnerability to break out to kernel context. This is typically the second stage in a complete device exploit chain: stage 1 exploits a WebKit/renderer bug for initial code execution in app context, stage 2 uses a kernel bug like CVE-2021-30807 for sandbox escape and persistence
• No user interaction after app launch: Once a malicious app is running, the kernel exploit executes without further user interaction
• Cross-platform: The vulnerability affects both mobile (iOS/iPadOS/watchOS) and desktop (macOS) due to shared IOMobileFrameBuffer code

Discovery

Reported by an anonymous researcher. Apple's security advisories for iOS 14.7.1 and macOS 11.5.1 stated the vulnerability "may have been actively exploited," confirming zero-day exploitation at the time of the patch.

Exploitation Context

IOMobileFrameBuffer zero-days are among the most valuable iPhone vulnerabilities — they provide the kernel access needed for complete device compromise. Commercial mobile spyware vendors (Pegasus, Predator, and others) and nation-state mobile exploitation teams routinely seek these kernel-level vulnerabilities to complete their iOS exploit chains. The emergency July 2021 out-of-band patch (separate from the regular monthly iOS update cycle) signals Apple's assessment that the risk of continued exploitation was high enough to warrant immediate action. CISA's November 2021 KEV addition (retroactively added well after the July patch) reflects the continued relevance of unpatched iOS devices and the confirmed exploitation record.

Remediation

1. Update iOS/iPadOS to 14.7.1 or later (Settings → General → Software Update)
2. Update macOS to Big Sur 11.5.1 or later, or upgrade to a later macOS release
3. Update watchOS to 7.6.1 or later (Watch app → General → Software Update)
4. Enable automatic software updates on all Apple devices: Settings → General → Software Update → Automatic Updates
5. For enterprise iOS fleet management: enforce minimum OS version via MDM (Mobile Device Management) policy and quarantine non-compliant devices