CVE-2021-31010

What it actually does

CVE-2021-31010 is an Apple operating system sandbox escape caused by unsafe deserialization and insufficient validation. A process already executing inside an Apple sandbox may be able to bypass sandbox restrictions and perform actions that should be denied by the sandbox policy. The vulnerability affects iOS, iPadOS, macOS, and watchOS and was addressed by Apple through improved validation in the affected deserialization path. On its own, the flaw is primarily an integrity impact: it does not provide initial code execution by itself, but it can allow malicious or compromised sandboxed code to reach resources, services, or operations outside its intended containment boundary.

Why it matters to the business

Successful exploitation can weaken one of the core containment controls used by Apple platforms, increasing the impact of a malicious app, compromised web content process, exploit chain, or other sandboxed component. In practical terms, it may allow an attacker to escalate from limited execution to broader device compromise when paired with another vulnerability. Apple reported that this issue may have been actively exploited at the time of release, and it is listed in CISA KEV with a remediation due date of 2022-09-15, making remediation historically urgent for any remaining unpatched or unsupported devices. Organizations with mobile fleets, macOS endpoints, or managed Apple devices may face elevated risk of data exposure, persistence, policy bypass, or further privilege escalation if outdated versions remain in service.

How an attack unfolds

An attacker typically needs a foothold inside a sandboxed process first, such as malicious application code, a compromised renderer process, a document or web-content exploit chain, or another vulnerability that obtains code execution in a constrained Apple process. From there, the attacker triggers the vulnerable deserialization behavior with crafted serialized data or interprocess input that is not validated correctly. If exploitation succeeds, the sandboxed process bypasses restrictions that would normally prevent access to protected services or operations. In real-world use, this type of bug is commonly chained with an initial remote code execution or local app exploit to move from limited sandboxed execution toward stronger control of the device. Apple indicated exploitation may have occurred in the wild at disclosure, so defenders should treat the vulnerability as a post-compromise capability used in targeted exploit chains rather than as a standalone network wormable issue.

How to fix it

Update affected Apple devices to a fixed or later operating system version. Apple fixed the issue in Security Update 2021-005 Catalina, iOS 12.5.5, iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6, and watchOS 7.6.2. Devices running versions older than these baselines should be upgraded immediately or removed from sensitive use if they cannot be updated. For macOS Catalina systems, apply Security Update 2021-005 Catalina or later applicable security updates. For iPhone and iPad, update to iOS/iPadOS 14.8 or later, or iOS 12.5.5 or later for supported older devices. For Apple Watch, update to watchOS 7.6.2 or later. As compensating controls, restrict installation of untrusted apps, enforce mobile device management compliance policies, disable or quarantine unsupported Apple OS versions, limit exposure to untrusted content, and monitor for signs of exploit-chain behavior on high-risk devices.

How to confirm the fix worked

Confirm that all affected Apple assets report an operating system version at or above the Apple fixed releases: macOS Big Sur 11.6 or later, macOS Catalina with Security Update 2021-005 or later, iOS 14.8 or later, iPadOS 14.8 or later, iOS 12.5.5 or later where applicable, and watchOS 7.6.2 or later. Use MDM inventory, endpoint management tooling, Apple software update status, and vulnerability management scans to identify outdated devices. On macOS, validate using system version and patch inventory data such as `sw_vers`, Software Update history, and installed security update records. On iOS, iPadOS, and watchOS, validate through device inventory and compliance posture rather than attempting exploit testing. Because public exploit validation may be unreliable and risky, do not attempt live exploitation on production devices; instead, verify patch level and confirm unsupported devices are isolated or retired.

Typical attack path

1. Gain or induce code execution in a sandboxed Apple process, such as through a malicious app, compromised web content process, or separate exploit.
2. Deliver crafted serialized data or invoke the vulnerable deserialization path from within that sandboxed context.
3. Abuse insufficient validation during deserialization to cause the operating system component or service to accept unsafe object state or messages.
4. Circumvent sandbox policy restrictions that would normally block access to protected resources, services, or operations.
5. Chain the sandbox escape with additional actions such as accessing sensitive data, invoking privileged services, staging persistence, or escalating further depending on the attacker’s objectives.

How to detect it

Detection should focus on signs that a sandboxed process escaped containment or was part of a broader exploit chain, because this vulnerability is not expected to produce a single definitive network signature. Review MDM and endpoint telemetry to identify devices that were unpatched when the issue was actively exploited. On macOS, examine Unified Logs, crash reports, Endpoint Security/EDR events, and process telemetry for sandbox denial anomalies followed by unexpected success, unusual access to protected resources, or sandboxed processes spawning unexpected child processes. Review crash logs for repeated failures in system services or sandboxed applications around suspicious documents, web browsing, messaging, or app execution. Look for unexpected execution from temporary directories, abnormal interprocess communication, suspicious XPC activity, and attempts by sandboxed apps to access files or services outside their expected profile. On iOS, iPadOS, and watchOS, detection is more limited; rely on MDM compliance history, device analytics/crash logs where available, unusual app behavior, unexpected configuration/profile changes, and network anomalies such as connections to known malicious infrastructure from devices that were unpatched. If high-risk devices were exposed, consider forensic acquisition using trusted mobile forensic workflows, preserving crash logs, sysdiagnose data, installed profile lists, app inventory, and network telemetry.

• Security Update 2021-005 Catalina
• iOS 12.5.5
• iOS 14.8
• iPadOS 14.8
• macOS Big Sur 11.6
• watchOS 7.6.2
• sandboxd
• Sandbox: deny
• com.apple.securityd
• com.apple.xpc
• /Library/Logs/DiagnosticReports/
• /Library/Logs/CrashReporter/
• /var/db/diagnostics/
• /private/var/mobile/Library/Logs/CrashReporter/
• /private/var/mobile/Library/Logs/CrashReporter/DiagnosticLogs/
• /private/var/tmp/
• /tmp/
• syspolicyd
• taskgated
• launchservicesd

What your security team should do

• Prioritize remediation for any Apple device running below the fixed versions, because the vulnerability is in CISA KEV and Apple reported possible active exploitation at disclosure.
• Use MDM or endpoint inventory to create an exception report for devices below iOS 14.8, iPadOS 14.8, iOS 12.5.5 for older supported devices, macOS Big Sur 11.6, macOS Catalina Security Update 2021-005, or watchOS 7.6.2.
• Remove, isolate, or restrict unsupported Apple devices that cannot receive the relevant security update.
• Hunt for evidence of chained exploitation, especially suspicious sandbox escapes, crashes in sandboxed processes, anomalous interprocess communication, unexpected child processes, and post-exploitation activity on devices that were unpatched during the exposure window.
• Increase scrutiny of devices used by high-risk users, executives, administrators, developers, journalists, or other targeted populations, because Apple sandbox escapes are often used in targeted exploit chains.
• Enforce controls that reduce initial footholds, including trusted app sources, application allowlisting where feasible, web protection, attachment filtering, and rapid browser/WebKit-related patching.
• Retain and review endpoint, MDM, crash, unified log, and network telemetry for the period when devices were unpatched, as sandbox escape exploitation may leave limited direct artifacts.