CVE-2021-30799 Overview
CVE-2021-30799 is a memory corruption vulnerability affecting Apple iOS, macOS Big Sur, macOS Catalina, and macOS Mojave. Processing maliciously crafted web content can lead to arbitrary code execution on affected devices. Apple addressed multiple memory corruption issues through improved memory handling in iOS 14.7, macOS Big Sur 11.5, Security Update 2021-004 Catalina, and Security Update 2021-005 Mojave. The flaw is classified as an out-of-bounds write [CWE-787] and carries network attack vector characteristics with user interaction required.
Critical Impact
Remote attackers can achieve arbitrary code execution by luring users to maliciously crafted web content, compromising confidentiality, integrity, and availability of affected Apple devices.
Affected Products
- Apple iOS (versions prior to 14.7)
- Apple macOS Big Sur (versions prior to 11.5)
- Apple macOS Catalina (prior to Security Update 2021-004) and macOS Mojave (prior to Security Update 2021-005)
Discovery Timeline
- 2021-09-08 - CVE-2021-30799 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2021-30799
Vulnerability Analysis
The vulnerability stems from multiple memory corruption issues within Apple's operating system components responsible for processing web content. An out-of-bounds write condition [CWE-787] allows attackers to write data beyond the boundaries of allocated memory buffers. When triggered through specially crafted web content, this corruption can be leveraged to overwrite adjacent memory structures, including function pointers and control flow data.
Successful exploitation results in arbitrary code execution within the context of the process handling the malicious content. Given the attack vector targets web content processing, exploitation typically occurs through Safari or applications using WebKit-based rendering. The EPSS score of 1.208% places this vulnerability in the 79th percentile for likelihood of exploitation.
Root Cause
The root cause involves improper memory handling during the parsing or rendering of crafted web content. Apple's advisory indicates the fixes addressed bounds checking and memory management routines, suggesting the original code failed to validate sizes or offsets before performing memory write operations. This category of flaw commonly arises in complex content parsers handling untrusted input.
Attack Vector
The attack vector is network-based and requires user interaction. An attacker hosts malicious content on a controlled website or delivers it through an embedded resource. When a victim visits the page or opens content rendered by a vulnerable component, the crafted payload triggers the memory corruption. No authentication or elevated privileges are required to launch the attack.
The vulnerability mechanism involves crafting web content that triggers out-of-bounds memory writes during parsing. Refer to the Apple Security Update HT212601 advisory for component-specific technical context.
Detection Methods for CVE-2021-30799
Indicators of Compromise
- Unexpected Safari or WebKit process crashes with memory access violations in system logs.
- Outbound connections from browser processes to unfamiliar domains following web content rendering.
- Spawning of shell processes or unsigned binaries by Safari, WebContent, or related child processes.
- Persistence artifacts in ~/Library/LaunchAgents/ or /Library/LaunchDaemons/ created shortly after browsing activity.
Detection Strategies
- Monitor endpoint telemetry for anomalous child processes spawned by browser and WebKit-based application processes.
- Inspect crash reports under ~/Library/Logs/DiagnosticReports/ for repeated EXC_BAD_ACCESS signatures tied to web content rendering.
- Correlate web browsing activity with subsequent file system or network anomalies on the same host.
Monitoring Recommendations
- Enable verbose logging for Safari, WebContent, and related XPC services to capture exploitation indicators.
- Track OS build versions across the fleet to identify endpoints running pre-patch versions of iOS 14.7 and macOS 11.5.
- Maintain network egress monitoring for connections to known malicious infrastructure following web sessions.
How to Mitigate CVE-2021-30799
Immediate Actions Required
- Update all Apple devices to iOS 14.7, macOS Big Sur 11.5, Security Update 2021-004 Catalina, or Security Update 2021-005 Mojave or later.
- Inventory endpoints running affected versions and prioritize patching for internet-facing and high-privilege users.
- Restrict browsing to untrusted websites on unpatched devices until updates are applied.
Patch Information
Apple released patches addressing this vulnerability across affected platforms. See vendor advisories: Apple Security Update HT212600, Apple Security Update HT212601, Apple Security Update HT212602, and Apple Security Update HT212603. Apply the corresponding update for each affected platform through Software Update.
Workarounds
- Disable JavaScript in Safari for users who cannot immediately apply patches, reducing the attack surface for crafted web content.
- Deploy enterprise content filtering to block access to suspicious or newly registered domains.
- Enforce least-privilege user accounts on macOS endpoints to limit impact of successful exploitation.
# Verify macOS version and apply pending updates
sw_vers -productVersion
sudo softwareupdate -l
sudo softwareupdate -ia --restart
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
