CVE-2024-40776: Apple iPhone OS Use-After-Free Flaw

CVE-2024-40776 Overview

CVE-2024-40776 is a use-after-free vulnerability affecting Apple's WebKit engine across multiple platforms including iOS, iPadOS, macOS, Safari, watchOS, tvOS, and visionOS. This memory management flaw occurs when processing maliciously crafted web content, which can lead to an unexpected process crash. The vulnerability was addressed through improved memory management in Apple's July 2024 security updates.

Critical Impact

Processing maliciously crafted web content may lead to an unexpected process crash, causing denial of service conditions across Apple devices and browsers using WebKit.

Affected Products

• Apple iOS (versions prior to 16.7.9 and 17.6)
• Apple iPadOS (versions prior to 16.7.9 and 17.6)
• Apple macOS Sonoma (versions prior to 14.6)
• Apple Safari (versions prior to 17.6)
• Apple watchOS (versions prior to 10.6)
• Apple tvOS (versions prior to 17.6)
• Apple visionOS (versions prior to 1.3)

Discovery Timeline

• July 29, 2024 - CVE-2024-40776 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2024-40776

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a type of memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of WebKit, this flaw exists within the web content processing engine, where improper memory management allows an attacker to trigger a use-after-free condition through specially crafted web content.

The attack requires user interaction—specifically, a victim must navigate to or be redirected to a malicious webpage containing the exploit payload. Once triggered, the vulnerability causes the affected process to crash, resulting in a denial of service condition. While the current assessment indicates the primary impact is availability (process crash), use-after-free vulnerabilities historically have potential for more severe exploitation including arbitrary code execution if the freed memory can be controlled by an attacker.

Root Cause

The root cause of CVE-2024-40776 lies in improper memory lifecycle management within WebKit's web content processing components. When certain operations are performed on web content, the code fails to properly track object lifetimes, leading to a scenario where memory is deallocated while still being referenced. This creates a dangling pointer that, when subsequently accessed, causes undefined behavior—in this case manifesting as a process crash.

Apple addressed this issue by implementing improved memory management techniques to ensure that object references are properly maintained throughout their lifecycle and that freed memory is no longer accessed.

Attack Vector

The attack vector for this vulnerability is network-based and requires user interaction. An attacker would need to:

1. Host malicious web content on a server or inject it into a legitimate website
2. Entice a victim to visit the malicious page through phishing, social engineering, or other redirection techniques
3. The victim's browser processes the crafted content, triggering the use-after-free condition
4. The WebKit process crashes, causing denial of service

The vulnerability can be exploited through Safari directly or any application that uses WebKit for rendering web content on affected Apple platforms.

Detection Methods for CVE-2024-40776

Indicators of Compromise

• Repeated unexpected Safari or WebKit process crashes when browsing certain websites
• Crash reports in system logs indicating memory access violations in WebKit components
• Unusual network connections to suspicious domains immediately before browser crashes
• ReportCrash processes spawning frequently for Safari or WebKit-related processes

Detection Strategies

• Monitor system crash logs (/Library/Logs/DiagnosticReports/) for WebKit-related crashes with memory access violation signatures
• Implement network security monitoring to detect connections to known malicious domains serving exploit content
• Deploy endpoint detection solutions capable of identifying abnormal WebKit process behavior patterns
• Utilize browser extension or proxy-based web filtering to block access to untrusted content sources

Monitoring Recommendations

• Enable comprehensive logging for Safari and WebKit processes on managed devices
• Configure SIEM solutions to alert on clusters of WebKit crash events across endpoints
• Monitor for unusual patterns of browser process restarts that may indicate exploitation attempts
• Review Apple's security advisories and update detection signatures accordingly

How to Mitigate CVE-2024-40776

Immediate Actions Required

• Update all Apple devices to the patched versions: iOS 16.7.9/17.6, iPadOS 16.7.9/17.6, Safari 17.6, macOS Sonoma 14.6, watchOS 10.6, tvOS 17.6, or visionOS 1.3
• Enable automatic updates on all Apple devices to ensure timely application of security patches
• Advise users to avoid visiting untrusted websites until patches are applied
• Review and restrict web browsing permissions for sensitive systems

Patch Information

Apple has released security updates addressing this vulnerability across all affected platforms. Patches are available through the following official Apple support documents:

• Apple Support Document HT214116 - iOS 17.6 and iPadOS 17.6
• Apple Support Document HT214117 - iOS 16.7.9 and iPadOS 16.7.9
• Apple Support Document HT214119 - Safari 17.6
• Apple Support Document HT214121 - watchOS 10.6
• Apple Support Document HT214122 - tvOS 17.6
• Apple Support Document HT214123 - visionOS 1.3
• Apple Support Document HT214124 - macOS Sonoma 14.6

Additionally, Debian has released updates for WebKitGTK packages as documented in the Debian LTS Announcement.

Workarounds

• Use alternative browsers that do not rely on WebKit for rendering until updates can be applied (limited applicability on iOS)
• Implement web content filtering at the network perimeter to block known malicious domains
• Enable Safari's built-in security features such as Fraudulent Website Warning
• Consider restricting JavaScript execution for untrusted sites using content blockers

# Check current Safari version on macOS
/usr/bin/defaults read /Applications/Safari.app/Contents/Info CFBundleShortVersionString

# Check iOS version via MDM or manually
# Settings > General > About > Software Version

# Force software update check on macOS
softwareupdate --list

# Install available updates
softwareupdate --install --all