Apple iOS WebKit Use-After-Free Vulnerability (CVE-2021-30762) Technical Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTLegacy Apple devices running iOS versions prior to 12.5.4 (including iPhone 5s, iPhone 6, iPad Air, iPad mini 2/3, and iPod touch 6th gen)
Processing maliciously crafted web content may trigger a Use-After-Free condition, leading to arbitrary code execution (RCE) and potential device compromise
Immediately update affected legacy iOS devices to version 12.5.4 or later, and restrict access to untrusted web links
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Users must immediately update their legacy iOS devices to version 12.5.4 or later via Over-The-Air (OTA) updates or iTunes/Finder.
# On-device update path:
# Settings -> General -> Software Update -> Download and Install iOS 12.5.4 or later2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, enforce MDM policies to restrict access to untrusted external websites and block vulnerable User-Agents at the reverse proxy level.
# Nginx configuration to block vulnerable legacy iOS User-Agents
map $http_user_agent $block_legacy_ios {
default 0;
~*"iPhone OS 12_[0-5]" 1;
~*"iPad; CPU OS 12_[0-5]" 1;
}
server {
listen 443 ssl;
if ($block_legacy_ios) {
return 403 'Access Denied: Please update your iOS device to 12.5.4+ to access corporate resources.';
}
}3. Log Audit & IoC Verification Commands
Use the following Python script to parse web server access logs and identify vulnerable legacy iOS devices connecting to your network infrastructure.
# Python script to audit web server logs for vulnerable iOS versions
import re
ua_pattern = re.compile(r'"(Mozilla/.*?iPhone OS (\d+)_(\d+)_?(\d+)?.*?)"')
with open('access.log', 'r') as log_file:
for line in log_file:
match = ua_pattern.search(line)
if match:
full_ua = match.group(1)
major = int(match.group(2))
minor = int(match.group(3))
patch = int(match.group(4)) if match.group(4) else 0
# Detect iOS versions below 12.5.4
if major < 12 or (major == 12 and (minor < 5 or (minor == 5 and patch < 4))):
print(f'[ALERT] Vulnerable iOS Client Detected: {full_ua}')Block Kernel Privilege Escalation & Ransomware Payloads Before You Can Reboot
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-30762) is a critical Use-After-Free (UAF) memory corruption flaw residing within the WebKit rendering engine of Apple iOS. The root cause lies in improper memory management when handling dynamic DOM elements or JavaScript objects. When WebKit fails to clear or nullify pointers to memory locations that have already been deallocated, an attacker can manipulate the heap layout to reuse these dangling pointers, leading to memory corruption.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a specially crafted web page containing malicious HTML/JavaScript. When a vulnerable iOS device visits the site via Safari or an embedded WebKit view, the script triggers the premature deallocation of a specific object and fills the freed memory slot with attacker-controlled shellcode. When WebKit subsequently attempts to access the freed object, it executes the attacker's payload instead, achieving arbitrary code execution under the context of the WebKit process.
3. Infrastructure & Business Impact
As this vulnerability is actively exploited in the wild and listed in the CISA KEV catalog, it poses a severe threat to enterprise environments. Successful exploitation allows remote attackers to compromise mobile endpoints, bypass sandbox boundaries when chained with local privilege escalation exploits, and gain unauthorized access to corporate networks, sensitive credentials, and internal communications.
Official Vendor Advisories & References
A use after free issue was addressed with improved memory management. This issue is fixed in iOS 12.5.4. 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-2021-30762)
FAQQ1. How critical is CVE-2021-30762 and is it actively exploited in the wild?
CVE-2021-30762 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 11.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-30762?
Primary impacted vendors include apple across ios, safari, webkit. Scope summary: Legacy Apple devices running iOS versions prior to 12.5.4
Q3. What temporary mitigations or workarounds exist for CVE-2021-30762 before patching?
[Mitigation] Immediately update affected legacy iOS devices to version 12.5.4 or later, and restrict access to untrusted web links Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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