CVE-2021-30883

What is IOMobileFrameBuffer?

IOMobileFrameBuffer is a kernel extension (kext) in iOS, iPadOS, macOS, watchOS, and tvOS responsible for managing the display frame buffer — the region of memory that stores the image currently displayed on screen. As a kernel-mode component that handles hardware-level display management, IOMobileFrameBuffer runs with the highest privilege level on Apple platforms. Memory corruption in IOMobileFrameBuffer can be exploited by a malicious app to break out of the iOS sandbox and achieve kernel code execution — bypassing all application-level security boundaries and allowing full device control. IOMobileFrameBuffer has been a recurring target in iOS exploit chains throughout 2021.

Overview

CVE-2021-30883 is an out-of-bounds write vulnerability (CWE-787) in the IOMobileFrameBuffer kernel extension, affecting iOS, iPadOS, macOS, watchOS, and tvOS. Apple patched this in iOS 15.0.2 / watchOS 8.0.1 on October 11, 2021, as an emergency out-of-band update, acknowledging "may have been actively exploited." A malicious application can exploit the memory corruption to execute arbitrary code with kernel privileges, breaking the iOS app sandbox and achieving complete device control. CISA added this to KEV in May 2022.

Affected Versions

Technical Details

• Root cause: Out-of-bounds write (CWE-787) in the IOMobileFrameBuffer kernel extension — the kernel component managing the display frame buffer performs an out-of-bounds write that corrupts kernel memory adjacent to the display buffer
• Kernel code execution: Exploiting the OOB write in a kernel extension achieves arbitrary kernel read/write and ultimately kernel code execution — the highest privilege level on iOS, bypassing all sandbox protections
• Attack vector: Local (AV:L) with no privileges required (PR:N) but user interaction required (UI:R) — a malicious app running on the device triggers the exploit, typically delivered as the second stage in a browser or iMessage exploit chain
• Device-level impact: Kernel code execution enables: disabling SEP protections, installing persistent spyware, accessing all on-device data (including encrypted messaging apps), activating camera and microphone, and surviving device restarts
• IOMobileFrameBuffer pattern: Multiple IOMobileFrameBuffer CVEs appeared in CISA KEV in 2021 (including CVE-2021-30807 patched in July), suggesting ongoing research focus on this kernel extension attack surface

Discovery

Reported to Apple and confirmed as a zero-day in the October 11, 2021 iOS 15.0.2 emergency release. The May 2022 CISA KEV addition reflects continued exploitation against devices running iOS versions prior to 15.0.2.

Exploitation Context

IOMobileFrameBuffer zero-days are high-value assets in iOS exploit chains because they provide the kernel escalation step needed to convert renderer-level code execution into complete device control. Apple's October 2021 emergency out-of-band patch for iOS 15 (which had just launched September 20, 2021 — meaning this zero-day was exploited against the freshly-released iOS 15 within three weeks of launch) demonstrates the rapid cadence at which advanced threat actors discover and weaponize new iOS attack surfaces. The CISA KEV addition seven months after the patch reflects exploitation against enterprise and government iOS fleets with slow update adoption.

Remediation

1. Update iOS/iPadOS to 15.0.2 or later — any current iOS release contains the fix
2. Update watchOS to 8.0.1 or later
3. Enable automatic software updates on all Apple devices: Settings → General → Software Update → Automatic Updates
4. For enterprise iOS fleet management: enforce minimum OS version policies via MDM (Mobile Device Management) and flag devices running iOS < 15.0.2 for immediate update
5. Run Lockdown Mode (iOS 16+) on devices belonging to high-risk individuals to reduce the attack surface available for IOMobileFrameBuffer-type exploits