CVE-2021-30799: Apple iPhone OS RCE Vulnerability

CVE-2021-30799 Overview

CVE-2021-30799 is a memory corruption vulnerability affecting Apple's iOS and macOS operating systems. The vulnerability exists within Apple's web content processing components, where multiple memory corruption issues allow attackers to execute arbitrary code on affected systems. When a user visits a maliciously crafted webpage, the vulnerability can be exploited to achieve remote code execution with the privileges of the current user.

Critical Impact

Processing maliciously crafted web content may lead to arbitrary code execution, potentially allowing attackers to gain full control of affected Apple devices including iPhones and Macs.

Affected Products

• Apple iOS versions prior to 14.7
• Apple macOS Big Sur versions prior to 11.5
• Apple macOS Catalina (requires Security Update 2021-004)
• Apple macOS Mojave (requires Security Update 2021-005)
• Apple Mac OS X versions 10.14.6 and 10.15.7 with various security update states

Discovery Timeline

• September 8, 2021 - CVE-2021-30799 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2021-30799

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption issue that occurs when software writes data past the boundaries of allocated memory. In the context of Apple's web content processing engine, the flaw allows malicious web content to corrupt memory in ways that can be leveraged for code execution.

The network-based attack vector requires user interaction, specifically visiting a malicious webpage or loading malicious web content within an application. Once triggered, the memory corruption can overwrite critical data structures, function pointers, or return addresses, enabling an attacker to redirect program execution to attacker-controlled code.

The vulnerability affects both mobile (iOS) and desktop (macOS) platforms, significantly expanding the attack surface across Apple's device ecosystem.

Root Cause

The root cause stems from improper memory handling within Apple's web content processing components. Specifically, the software fails to adequately validate or constrain memory operations when processing certain types of web content, leading to out-of-bounds write conditions.

When the web rendering engine processes specially crafted content, it can write data beyond the intended memory buffer boundaries. This out-of-bounds write corrupts adjacent memory regions, which an attacker can exploit to gain control over program execution flow.

Attack Vector

The attack is network-based and requires user interaction. An attacker must convince a victim to visit a malicious website or interact with web content containing the exploit payload. The attack scenario typically involves:

1. Attacker hosts malicious web content on a controlled server or compromises a legitimate website
2. Victim navigates to the malicious content using Safari or another application that renders web content
3. The malicious content triggers the memory corruption vulnerability
4. The attacker achieves arbitrary code execution in the context of the vulnerable process

The exploitation does not require authentication or special privileges, making it accessible to remote attackers who can lure victims to malicious web content.

Detection Methods for CVE-2021-30799

Indicators of Compromise

• Unusual WebKit or Safari process crashes followed by unexpected system behavior
• Network connections to suspicious domains immediately after browsing activity
• Unexpected child processes spawned from web browser or web content processes
• Memory allocation anomalies or crash reports indicating out-of-bounds memory access

Detection Strategies

• Monitor for WebKit-related crash reports that indicate memory corruption patterns
• Implement network-based detection for known malicious web content patterns
• Use endpoint detection solutions to monitor browser process behavior and child process creation
• Review system logs for unexpected code execution or privilege escalation following web browsing

Monitoring Recommendations

• Enable enhanced logging for Safari and other WebKit-based applications
• Configure SentinelOne agents to monitor for suspicious process creation chains from browser processes
• Implement URL filtering to block access to known malicious domains serving exploit kits
• Monitor for post-exploitation behaviors such as unauthorized data access or persistence mechanisms

How to Mitigate CVE-2021-30799

Immediate Actions Required

• Update iOS devices to version 14.7 or later immediately
• Update macOS Big Sur systems to version 11.5 or later
• Apply Security Update 2021-004 for macOS Catalina systems
• Apply Security Update 2021-005 for macOS Mojave systems
• Prioritize updates for devices used to access untrusted web content

Patch Information

Apple has released patches addressing this vulnerability across multiple product lines. The fixes implement improved memory handling to prevent the out-of-bounds write conditions:

• Apple Support Document HT212600 - iOS 14.7 security content
• Apple Support Document HT212601 - macOS Big Sur 11.5 security content
• Apple Support Document HT212602 - Security Update 2021-004 Catalina
• Apple Support Document HT212603 - Security Update 2021-005 Mojave

Workarounds

• Restrict web browsing to trusted sites only until patches can be applied
• Consider using alternative non-WebKit browsers as a temporary mitigation
• Implement web content filtering at the network level to block potentially malicious content
• Enable content blockers and disable JavaScript execution on untrusted websites where feasible

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# Settings > General > About > Software Version

# Check current macOS version
sw_vers -productVersion

# Verify macOS security updates applied
softwareupdate --history