CVE-2021-30762: Apple iPhone OS Use After Free Vulnerability

CVE-2021-30762 Overview

CVE-2021-30762 is a use after free vulnerability in Apple iOS that enables arbitrary code execution through the processing of maliciously crafted web content. This memory corruption flaw exists in the WebKit browser engine and has been actively exploited in the wild. Apple addressed the vulnerability with improved memory management in iOS 12.5.4.

Critical Impact

This vulnerability has been actively exploited in the wild and is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, requiring immediate attention for organizations running affected iOS versions.

Affected Products

• Apple iPhone OS versions prior to 12.5.4
• Older iPhone devices running iOS 12.x (iPhone 5s, iPhone 6, iPhone 6 Plus)
• Older iPad devices running iOS 12.x

Discovery Timeline

• 2021-09-08 - CVE-2021-30762 published to NVD
• 2025-10-23 - Last updated in NVD database

Technical Details for CVE-2021-30762

Vulnerability Analysis

This use after free vulnerability occurs in Apple's WebKit browser engine, which is the core rendering component for Safari and all web content displayed on iOS devices. Use after free conditions arise when an application continues to reference memory after it has been freed, leading to memory corruption that can be leveraged for code execution.

In the context of CVE-2021-30762, the vulnerability can be triggered when a user visits a malicious website or opens web content that has been specifically crafted to exploit this memory management flaw. The attacker-controlled web content manipulates WebKit's internal memory handling, creating a condition where freed memory is subsequently accessed. By carefully controlling the contents of this memory region, an attacker can redirect program execution and achieve arbitrary code execution with the privileges of the WebKit process.

Apple has acknowledged reports that this vulnerability has been actively exploited, indicating its use in real-world attacks targeting iOS users. The inclusion in CISA's Known Exploited Vulnerabilities catalog further underscores the severity and active threat this vulnerability poses.

Root Cause

The root cause of CVE-2021-30762 is improper memory management within the WebKit engine (CWE-416: Use After Free). When processing certain web content, WebKit fails to properly track object lifecycles, resulting in a dangling pointer that references memory that has already been deallocated. Subsequent operations that dereference this pointer allow attackers to manipulate program state and achieve code execution.

Attack Vector

The attack vector is network-based, requiring user interaction to visit a malicious webpage or process attacker-controlled web content. An attacker could distribute malicious links through phishing emails, compromised advertisements (malvertising), watering hole attacks on legitimate websites, or direct messages. When a victim accesses the malicious content using a vulnerable iOS device, the exploit triggers the use after free condition, potentially leading to complete device compromise.

The vulnerability mechanism exploits WebKit's memory management subsystem. When specific sequences of DOM manipulations or JavaScript operations are performed, the engine incorrectly frees an object while retaining references to it. The subsequent use of this freed memory creates an exploitable condition. Technical details regarding specific exploitation methods can be found in the Apple Support Article.

Detection Methods for CVE-2021-30762

Indicators of Compromise

• Unexpected Safari or WebKit crashes followed by suspicious device behavior
• Evidence of web-based attacks in browser history or network traffic logs
• Unusual network connections from iOS devices to unknown external servers
• Device behavior anomalies such as unexpected battery drain or performance degradation

Detection Strategies

• Monitor MDM (Mobile Device Management) solutions for iOS devices running versions prior to 12.5.4
• Implement network-level inspection to detect known exploit delivery mechanisms
• Review proxy logs for connections to suspicious domains that may host exploit payloads
• Deploy endpoint detection solutions capable of identifying post-exploitation activity on iOS devices

Monitoring Recommendations

• Enable comprehensive logging for all managed iOS devices through enterprise MDM solutions
• Monitor for unusual outbound network traffic patterns from iOS devices
• Implement web filtering to block access to known malicious domains
• Regularly audit device software versions to ensure compliance with patching requirements

How to Mitigate CVE-2021-30762

Immediate Actions Required

• Update all affected iOS devices to version 12.5.4 or later immediately
• For devices that cannot be updated, consider restricting web browsing capabilities
• Notify users of older iPhone and iPad devices about the critical security update
• Review CISA's KEV catalog entry for additional guidance and compliance requirements

Patch Information

Apple has released iOS 12.5.4 to address this vulnerability along with two other security issues (CVE-2021-30761 and CVE-2021-30759). Organizations should deploy this update to all affected devices immediately. The security update includes improved memory management to properly handle object lifecycles and prevent the use after free condition.

For detailed patch information, refer to the Apple Support Article HT212548. Organizations subject to CISA directives should consult the CISA Known Exploited Vulnerabilities Catalog for compliance requirements.

Workarounds

• Restrict web browsing on vulnerable devices to trusted sites only if immediate patching is not possible
• Use content filtering proxies to inspect and sanitize web traffic before it reaches iOS devices
• Consider disabling JavaScript in Safari settings as a temporary measure (note: this may break site functionality)
• Implement network segmentation to isolate older iOS devices that cannot be updated

# MDM Configuration: Check iOS version compliance
# Example device query for version verification
# Devices should report iOS version >= 12.5.4

# For organizations using Apple Configurator or MDM:
# 1. Create a compliance policy requiring iOS 12.5.4 minimum
# 2. Deploy update notification to affected devices
# 3. Monitor compliance dashboard for non-compliant devices
# 4. Consider restricting network access for non-compliant devices