Apple iOS, iPadOS, and macOS WebKit Logic Issue Remote Code Execution Vulnerability (CVE-2021-1871)
Executive & SecOps Summary
SECOPS ASSESSMENTSystems running iOS versions prior to 14.4, iPadOS versions prior to 14.4, macOS Big Sur versions prior to 11.2, and Catalina/Mojave without Security Update 2021-001
A remote attacker can execute arbitrary code on the target system, and active exploitation in the wild has been reported
Immediately apply the official Apple software updates to upgrade to iOS/iPadOS 14.4, macOS Big Sur 11.2, or later
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
To mitigate this vulnerability, immediately update your Apple operating systems to the patched versions.
On macOS, run the following commands in the terminal to check and apply updates:
# Check for available software updates
softwareupdate -l
# Download and install all critical security updates and restart if necessary
sudo softwareupdate -iaR2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, restrict access to untrusted websites and enforce strict browser policies via Mobile Device Management (MDM) solutions.
You can disable JavaScript or restrict web features using an MDM configuration profile payload snippet:
<key>PayloadContent</key>
<array>
<dict>
<key>PayloadType</key>
<string>com.apple.webclip</string>
<key>safariAcceptCookies</key>
<integer>1</integer>
<key>enableJavaScript</key>
<false/>
</dict>
</array>3. Log Audit & IoC Verification Commands
Use the following shell script to audit the current macOS version and determine if the system is vulnerable:
#!/bin/bash
# Script to verify macOS version vulnerability status
os_version=$(sw_vers -productVersion)
echo 'Current macOS Version: ' $os_version
if [[ '$os_version' == 11.0* || '$os_version' == 11.1* ]]; then
echo '[WARNING] System is vulnerable to CVE-2021-1871. Please update to Big Sur 11.2 or later immediately.'
elif [[ '$os_version' == 10.15* || '$os_version' == 10.14* ]]; then
echo '[ATTENTION] Catalina/Mojave detected. Ensure Security Update 2021-001 is applied.'
else
echo '[SAFE] System is running a non-vulnerable or updated OS version.'
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2021-1871) stems from a logic validation issue within the WebKit rendering engine used across Apple's iOS, iPadOS, and macOS platforms. Due to insufficient restrictions and validation logic during input processing, untrusted remote content can bypass sandbox boundaries and execute within the context of the rendering process.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by hosting a maliciously crafted web page containing specialized scripts designed to trigger the logic flaw in WebKit. When a user visits the malicious site via Safari or any WebKit-based application, the logic validation fails, allowing the attacker's payload to bypass security restrictions and execute arbitrary code with the user's privileges.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 (Critical) and its inclusion in the CISA KEV catalog, this vulnerability poses an immediate threat to enterprise environments. Successful exploitation allows attackers to compromise employee endpoints, steal sensitive corporate data, and establish a persistent foothold within the internal corporate network.
Official Vendor Advisories & References
A logic issue was addressed with improved restrictions. This issue is fixed in macOS Big Sur 11.2, Security Update 2021-001 Catalina, Security Update 2021-001 Mojave, iOS 14.4 and iPadOS 14.4. A remote attacker may be able to cause arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited..
Frequently Asked SecOps Questions (CVE-2021-1871)
FAQQ1. How critical is CVE-2021-1871 and is it actively exploited in the wild?
CVE-2021-1871 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 7.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2021-1871?
Primary impacted vendors include apple across macos, ios, ipados, webkit. Scope summary: iOS and iPadOS versions prior to 14.4, macOS Big Sur versions prior to 11.2, and macOS Catalina/Mojave prior to Security Update 2021-001
Q3. What temporary mitigations or workarounds exist for CVE-2021-1871 before patching?
[Mitigation] Immediately apply the official Apple software updates to upgrade to iOS/iPadOS 14.4, macOS Big Sur 11.2, or later Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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