CVE-2021-31010: Apple iPadOS Privilege Escalation Flaw

CVE-2021-31010 Overview

CVE-2021-31010 is a deserialization vulnerability affecting multiple Apple operating systems, including iOS, iPadOS, macOS Catalina, macOS Big Sur, and watchOS. The flaw allows a sandboxed process to circumvent sandbox restrictions through improper validation of serialized data. Apple confirmed awareness of reports indicating active exploitation at the time of the security update release. CISA has added this vulnerability to its Known Exploited Vulnerabilities (KEV) catalog. The issue is tracked as [CWE-502] Deserialization of Untrusted Data and was addressed through improved validation in Security Update 2021-005 Catalina, iOS 12.5.5, iOS 14.8, iPadOS 14.8, macOS Big Sur 11.6, and watchOS 7.6.2.

Critical Impact
A sandboxed process can bypass macOS and iOS sandbox restrictions, breaking a core Apple security boundary that isolates untrusted code from sensitive system resources.

Affected Products

Apple iOS 12.x prior to 12.5.5 and iOS 14.x prior to 14.8
Apple iPadOS prior to 14.8, macOS Big Sur prior to 11.6, and macOS Catalina without Security Update 2021-005
Apple watchOS prior to 7.6.2

Discovery Timeline

2021-08-24 - CVE-2021-31010 published to the National Vulnerability Database
2025-10-23 - Last updated in NVD database

Technical Details for CVE-2021-31010

Vulnerability Analysis

The vulnerability resides in how Apple operating systems deserialize data passed across the sandbox boundary. Sandboxed processes on iOS and macOS rely on strict input validation when interacting with privileged services through XPC and similar inter-process communication mechanisms. When deserialization routines fail to validate object types or contents, a malicious sandboxed process can craft serialized payloads that influence the receiving service in unintended ways. The result is sandbox escape — a violation of the integrity boundary that Apple uses to contain untrusted code, browser content, and third-party applications.

Root Cause

The root cause is insufficient validation during deserialization of untrusted input crossing trust boundaries, classified as [CWE-502]. Apple addressed the flaw by adding stricter validation to the affected deserialization paths.

Attack Vector

The attack requires code execution inside a sandboxed process, which an attacker typically obtains through a prior vulnerability such as a browser or media-parsing bug. Once inside the sandbox, the attacker sends malformed serialized objects to a privileged endpoint to escape sandbox containment and access resources outside the sandbox profile. CISA KEV listing indicates the chain has been used in real-world attacks.

No public proof-of-concept code is available. See the Apple Security Update HT212807 for vendor technical guidance.

Detection Methods for CVE-2021-31010

Indicators of Compromise

Unexpected child processes spawned from sandboxed applications such as browsers, mail clients, or media handlers
Sandboxed processes performing XPC calls to privileged services followed by file access outside their container
Anomalous crash reports referencing deserialization or XPC handlers on unpatched iOS, iPadOS, macOS, or watchOS devices

Detection Strategies

Inventory Apple endpoints and flag any device running iOS below 14.8, iPadOS below 14.8, macOS Big Sur below 11.6, macOS Catalina without Security Update 2021-005, or watchOS below 7.6.2
Correlate process lineage telemetry to identify sandboxed processes followed by activity that suggests escape, such as access to user data outside the app container
Monitor for exploitation chains that pair browser or messaging bugs with sandbox escape behavior

Monitoring Recommendations

Forward endpoint process and IPC telemetry from macOS hosts to a centralized analytics platform for retrospective hunting
Establish alerts for outdated Apple OS versions reporting to MDM or asset management systems
Review CISA KEV bulletins for related Apple sandbox escape vulnerabilities that may be chained

How to Mitigate CVE-2021-31010

Immediate Actions Required

Update iPhone and iPad devices to iOS 14.8 or iOS 12.5.5 and iPadOS 14.8 as applicable
Update macOS Big Sur devices to 11.6 and apply Security Update 2021-005 to macOS Catalina systems
Update Apple Watch devices to watchOS 7.6.2 and confirm patch deployment through MDM
Prioritize patching for high-risk users such as executives, journalists, and administrators given confirmed in-the-wild exploitation

Patch Information

Apple released fixes in iOS 12.5.5, iOS 14.8, iPadOS 14.8, macOS Big Sur 11.6, Security Update 2021-005 Catalina, and watchOS 7.6.2. Refer to Apple Security Update HT212804, HT212805, HT212806, HT212807, and HT212824 for version-specific details.

Workarounds

No vendor-supplied workaround exists; patching is the only supported remediation
Restrict installation of untrusted third-party applications and disable browsing on unpatched devices until updates are applied
Enforce minimum OS version policies through MDM to block non-compliant devices from accessing corporate resources

bash

# Verify patched macOS build via terminal
sw_vers -productVersion
# Expected output: 11.6 or later for Big Sur, 10.15.7 with Security Update 2021-005 for Catalina

# Verify iOS/iPadOS version via MDM query or Settings > General > About
# Required: 14.8 or 12.5.5 (legacy devices) or later