CVE-2021-30761 Overview
CVE-2021-30761 is a memory corruption vulnerability affecting Apple iOS devices. The vulnerability exists due to improper state management in the WebKit browser engine. When a user processes maliciously crafted web content, the vulnerability can be exploited to achieve arbitrary code execution on the affected device. Apple has confirmed awareness of reports that this vulnerability has been actively exploited in the wild.
Critical Impact
This vulnerability enables remote arbitrary code execution through malicious web content and has been confirmed as actively exploited in the wild. CISA has added this vulnerability to their Known Exploited Vulnerabilities (KEV) catalog.
Affected Products
- Apple iPhone OS versions prior to 12.5.4
- Devices running iOS 12.x that have not been updated
Discovery Timeline
- 2021-09-08 - CVE-2021-30761 published to NVD
- 2025-10-23 - Last updated in NVD database
Technical Details for CVE-2021-30761
Vulnerability Analysis
This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption issue stemming from improper state management within the WebKit rendering engine. The flaw allows attackers to corrupt memory in a controlled manner, ultimately enabling arbitrary code execution within the context of the vulnerable application.
The vulnerability is exploitable over the network and requires user interaction—specifically, the victim must navigate to or be redirected to attacker-controlled web content. Once triggered, successful exploitation grants the attacker the ability to execute arbitrary code with the privileges of the WebKit process, potentially compromising the entire device.
Given Apple's confirmation of active exploitation and its inclusion in CISA's Known Exploited Vulnerabilities catalog, this vulnerability represents a significant threat to organizations with unpatched iOS 12.x devices in their environment.
Root Cause
The root cause of CVE-2021-30761 lies in improper state management within WebKit's memory handling routines. When processing specific sequences of web content, the browser engine fails to properly track and validate memory state, leading to out-of-bounds write conditions. This memory corruption can be leveraged by attackers to overwrite critical data structures and redirect program execution flow.
Attack Vector
The attack vector for this vulnerability is network-based, requiring the target user to interact with malicious web content. Exploitation scenarios include:
- Watering Hole Attacks: Compromising legitimate websites frequented by target victims
- Phishing Campaigns: Sending links to malicious websites via email, SMS, or messaging applications
- Malvertising: Injecting malicious content through compromised advertising networks
- Drive-by Downloads: Exploiting the vulnerability through embedded content on seemingly benign web pages
The vulnerability's exploitation through Safari or any WebKit-based browser makes it particularly dangerous, as users may be compromised simply by visiting a malicious webpage.
Detection Methods for CVE-2021-30761
Indicators of Compromise
- Unexpected Safari or WebKit process crashes followed by unusual system behavior
- Suspicious network connections to unknown domains immediately following web browsing activity
- Anomalous memory allocation patterns in WebKit processes
- Unauthorized process spawning from Safari or other WebKit-based applications
Detection Strategies
- Monitor for WebKit crash reports and analyze crash dumps for signs of memory corruption exploitation
- Implement network traffic analysis to identify connections to known malicious infrastructure
- Deploy endpoint detection solutions capable of identifying memory corruption attack patterns
- Review MDM logs for devices exhibiting unusual behavior patterns post-browsing activity
Monitoring Recommendations
- Enable enhanced logging on iOS devices where possible through MDM solutions
- Configure alerts for devices connecting to URLs associated with known exploit delivery infrastructure
- Establish baseline behavioral patterns for Safari processes to detect anomalies
- Monitor for updates to CISA's KEV catalog for additional indicators related to this vulnerability
How to Mitigate CVE-2021-30761
Immediate Actions Required
- Update all iOS 12.x devices to iOS 12.5.4 or later immediately
- Prioritize patching for devices belonging to high-value targets such as executives and IT administrators
- Consider temporary restrictions on web browsing for critical devices until patched
- Review device inventory to identify all iOS 12.x devices requiring updates
Patch Information
Apple has addressed this vulnerability in iOS 12.5.4. Organizations should apply this update immediately given the confirmed active exploitation. For detailed patch information, refer to the Apple Support Article HT212548.
Due to the inclusion of this vulnerability in CISA's Known Exploited Vulnerabilities Catalog, federal agencies are required to remediate this vulnerability within specified timeframes under Binding Operational Directive 22-01.
Workarounds
- Restrict web browsing on vulnerable devices to trusted internal sites only until patches can be applied
- Implement web content filtering to block access to known malicious domains
- Consider deploying alternative browsers that do not rely on WebKit for critical browsing needs
- Enable content blockers where available to reduce exposure to malicious web content
# Verify iOS version via MDM query
# Devices should report iOS 12.5.4 or later
# Example: Check device inventory for vulnerable versions
mdm query --devices --filter "os_version < 12.5.4" --output vulnerable_devices.csv
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
