Apple WebKit Use-After-Free Remote Code Execution Vulnerability (CVE-2021-30858) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTApple WebKit-based browsers and applications running on iOS versions prior to 14.8, iPadOS versions prior to 14.8, and macOS Big Sur versions prior to 11.6
Processing maliciously crafted web content may allow remote attackers to trigger a Use-After-Free condition, leading to arbitrary code execution (RCE) on the target system
Immediately apply the official Apple software updates to upgrade to iOS/iPadOS 14.8, macOS Big Sur 11.6, or later
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
To remediate this vulnerability, apply the official security updates provided by Apple. For enterprise environments managing macOS fleets, the update can be enforced remotely via MDM or terminal execution:
# Check for available software updates and install all critical updates including OS patches
sudo softwareupdate -i -a --restart2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to untrusted external websites and enforce strict network-level filtering. On macOS, you can enable the application firewall to harden the network posture:
# Enable the built-in macOS Application Firewall
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on3. Log Audit & IoC Verification Commands
Use the following script to audit the current macOS version and verify if the system is running a vulnerable build:
# Retrieve current macOS product version and build metadata
CURRENT_VER=$(sw_vers -productVersion)
CURRENT_BUILD=$(sw_vers -buildVersion)
echo 'Detected macOS Version:' $CURRENT_VER 'Build:' $CURRENT_BUILD
# Check if the system is running a vulnerable Big Sur version (below 11.6)
if [[ '$CURRENT_VER' == 11.* ]]; then
minor_ver=$(echo $CURRENT_VER | cut -d. -f2)
if [ '$minor_ver' -lt 6 ]; then
echo '[ALERT] Vulnerable macOS version detected. CVE-2021-30858 mitigation required.'
else
echo '[INFO] System is running a patched version.'
fi
fiBlock Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
Protect unpatched Windows, Linux, and macOS workloads against in-memory exploitation and lateral movement with autonomous EDR.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-30858) is a critical Use-After-Free (UAF) flaw residing within Apple's WebKit rendering engine. Due to improper memory management during the lifecycle handling of specific DOM or JavaScript binding objects, the engine fails to clear object references after they have been deallocated from memory. This leaves dangling pointers that, when subsequently accessed or manipulated, allow attackers to corrupt the application's memory space.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a specially crafted web page containing malicious HTML or JavaScript. When a victim visits the malicious site using Safari or any application utilizing the WebKit framework, the engine processes the crafted content, triggering premature memory deallocation of a target object. The attacker then uses heap spraying or similar memory layout manipulation techniques to overwrite the freed memory location with controlled shellcode, hijacking the control flow when the dangling pointer is dereferenced.
3. Infrastructure & Business Impact
As this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, it poses an immediate threat to enterprise environments. Successful exploitation requires minimal user interaction (drive-by download scenario) and can lead to complete compromise of the endpoint. This could serve as an initial entry point for threat actors to pivot into internal corporate networks, exfiltrate sensitive data, or deploy ransomware.
Official Vendor Advisories & References
A use after free issue was addressed with improved memory management. This issue is fixed in iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.
Frequently Asked SecOps Questions (CVE-2021-30858)
FAQQ1. How critical is CVE-2021-30858 and is it actively exploited in the wild?
CVE-2021-30858 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 13.4%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-30858?
Primary impacted vendors include apple across safari, webkit, ios, ipados, macos. Scope summary: iOS < 14.8, iPadOS < 14.8, macOS Big Sur < 11.6
Q3. What temporary mitigations or workarounds exist for CVE-2021-30858 before patching?
[Mitigation] Immediately apply the official Apple software updates to upgrade to iOS/iPadOS 14.8, macOS Big Sur 11.6, or later Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2021-30858
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (apple)
View Category →Apple iOS, macOS, and watchOS Memory Corruption Arbitrary Code Execution Vulnerability (CVE-2026-20700)
[Affected Scope] Apple devices running iOS before 26.3, iPadOS before 26.3, macOS Tahoe before 26.3, tvOS before 26.3, visionOS before 26.3, and watchOS before 26.3
Apple iOS and macOS Out-of-bounds Write Remote Code Execution Vulnerability (CVE-2026-86950) Security Advisory
[Affected Scope] All Apple devices running versions prior to iOS 18.7.11/26.7.1 and macOS Sequoia 15.8.1/Tahoe 26.7.1.
Apple macOS Screen Sharing Authentication Bypass Vulnerability (CVE-2026-65400)
[Affected Scope] macOS systems running versions prior to Sequoia 15.7.9, Sonoma 14.8.9, Tahoe 26.6.1/26.7, or Golden Gate 27 with Screen Sharing or VNC services enabled
Google Chrome Dawn Use-After-Free Vulnerability (CVE-2026-5281) Technical Advisory
[Affected Scope] Google Chrome versions prior to 146.0.7680.178
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.