Apple iOS WebKit Buffer Overflow Remote Code Execution Vulnerability (CVE-2021-30666) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTApple devices running iOS versions prior to 12.5.3 (including iPhone 5s, iPhone 6, iPad Air, iPad mini 2, iPad mini 3, and iPod touch 6th generation)
Processing maliciously crafted web content may allow remote attackers to trigger a buffer overflow, leading to arbitrary code execution and complete device compromise
Immediately update affected devices to iOS 12.5.3 or later to apply the official security patch
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Users must update their devices to iOS 12.5.3 or later via OTA updates or iTunes/Finder. For enterprise environments, MDM administrators can push the update command using the following payload structure:
<!-- MDM OS Update Command Payload -->
<dict>
<key>RequestType</key>
<string>ScheduleOSUpdate</string>
<key>Updates</key>
<array>
<dict>
<key>ProductKey</key>
<string>iOS12.5.3_Patch</string>
<key>InstallAction</key>
<string>Default</string>
</dict>
</array>
</dict>2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to untrusted websites using secure web gateways (SWG) or proxy servers. Disable JavaScript on untrusted networks to minimize the attack surface.
# Example Squid Proxy ACL to restrict outbound traffic to trusted domains only
acl Allowed_Domains dstdomain .company.com .apple.com
http_access allow Allowed_Domains
http_access deny all3. Log Audit & IoC Verification Commands
Analyze device crash logs and network traffic for signs of WebKit instability or connections to suspicious domains. Use the following command to search for WebKit-related memory access exceptions in extracted logs:
# Search for WebKit memory corruption crash signatures in extracted logs
grep -r 'Exception Type: EXC_BAD_ACCESS' ./CrashLogs/ | grep 'WebKit'Block 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-2021-30666) is a critical memory corruption issue within the WebKit rendering engine of Apple iOS. The root cause lies in improper memory handling and lack of validation when processing web content. This deficiency allows an attacker to trigger a buffer overflow, corrupting the application's memory space and hijacking control flow.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a specially crafted web page containing malicious HTML or JavaScript. When a target user visits the malicious site via Safari or any WebKit-based browser, the engine fails to handle the input safely, causing a buffer overflow. This enables the attacker to execute arbitrary shellcode within the context of the browser process, potentially bypassing sandbox restrictions.
3. Infrastructure & Business Impact
As this vulnerability is confirmed to have been actively exploited in the wild, it poses a severe threat to enterprise environments. Compromised mobile devices can serve as entry points for lateral movement within corporate networks, leading to credential theft, session hijacking, and unauthorized access to sensitive corporate resources.
Official Vendor Advisories & References
A buffer overflow issue was addressed with improved memory handling. This issue is fixed in iOS 12.5.3. 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-2021-30666)
FAQQ1. How critical is CVE-2021-30666 and is it actively exploited in the wild?
CVE-2021-30666 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 3.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-30666?
Primary impacted vendors include apple across ios, webkit. Scope summary: Apple devices running iOS versions prior to 12.5.3 (iPhone 5s, iPhone 6, iPhone 6 Plus, iPad Air, iPad mini 2, iPad mini 3, and iPod touch 6th generation)
Q3. What temporary mitigations or workarounds exist for CVE-2021-30666 before patching?
[Mitigation] Immediately update affected devices to iOS 12.5.3 or later to apply the official security patch 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-2021-30666
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