Apple macOS and iOS XNU Kernel Memory Information Disclosure Vulnerability (CVE-2020-27950)
Executive & SecOps Summary
SECOPS ASSESSMENTApple devices running macOS Big Sur prior to 11.0.1, iOS/iPadOS prior to 14.2, and watchOS prior to 7.1
A local attacker can execute a malicious application to disclose sensitive kernel memory, allowing them to bypass Kernel Address Space Layout Randomization (KASLR) and facilitate subsequent privilege escalation
Apply the official security updates provided by Apple to upgrade the operating system to the latest patched version
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
To mitigate this vulnerability, update the operating system to the latest secure version. In enterprise environments, administrators can force updates remotely using MDM solutions or via the command line on macOS:
# Check for available macOS updates and install them
sudo softwareupdate --list
sudo softwareupdate --install --all --restart2. Temporary Workaround & Hardening Configuration
Because this is a kernel-level vulnerability, there is no direct workaround other than patching. However, you can restrict the execution of untrusted applications by enforcing strict Gatekeeper policies:
# Enable Gatekeeper to prevent execution of unsigned applications
sudo spctl --master-enable
# Restrict execution of unapproved kernel extensions
sudo spctl --kext-consent disable3. Log Audit & IoC Verification Commands
Use the following script to check the current macOS version and determine if the system requires immediate patching:
# Retrieve macOS system version details
sw_vers
# Check kernel major version to identify potential vulnerability status
KERNEL_MAJOR=$(uname -r | cut -d. -f1)
if [ '$KERNEL_MAJOR' -lt 20 ]; then
echo '[ALERT] This system is running an unpatched kernel and may be vulnerable to CVE-2020-27950.'
else
echo '[OK] Kernel version is 20 or higher (macOS Big Sur 11.0.1+ equivalent).'
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-27950) is a memory initialization issue (CWE-665) residing within the Mach message trailers handling mechanism of the Apple XNU kernel. When copying data structures from kernel space to user space, certain padding bytes or uninitialized structure fields are not properly cleared, leading to the leakage of residual kernel stack or heap memory contents to user-space processes.
2. Exploitation Mechanics & Attack Scenario
An attacker with local access executes a specially crafted, non-privileged application on the target device. The application initiates communication with the kernel via Mach ports, requesting specific messages that trigger the generation of Mach message trailers. Due to the lack of proper initialization, the returned trailer contains raw kernel memory bytes. By parsing this leaked data, the attacker can extract kernel pointers, effectively defeating Kernel Address Space Layout Randomization (KASLR) and paving the way for local privilege escalation (LPE) exploits.
3. Infrastructure & Business Impact
As this vulnerability is listed in the CISA KEV catalog, it has been actively exploited in the wild. While a memory disclosure vulnerability does not directly allow code execution on its own, it serves as a critical prerequisite for reliable kernel-level exploitation. When chained with other vulnerabilities, it can lead to complete compromise of the endpoint, posing a severe threat to enterprise data confidentiality and infrastructure integrity.
Official Vendor Advisories & References
A memory initialization issue was addressed. This issue is fixed in macOS Big Sur 11.0.1, watchOS 7.1, iOS 12.4.9, watchOS 6.2.9, Security Update 2020-006 High Sierra, Security Update 2020-006 Mojave, iOS 14.2 and iPadOS 14.2, watchOS 5.3.9, macOS Catalina 10.15.7 Supplemental Update, macOS Catalina 10.15.7 Update. A malicious application may be able to disclose kernel memory.
Frequently Asked SecOps Questions (CVE-2020-27950)
FAQQ1. How critical is CVE-2020-27950 and is it actively exploited in the wild?
CVE-2020-27950 is rated CVSS 5.5 (MEDIUM) with a 30-day EPSS exploitation probability of 16.5%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-27950?
Primary impacted vendors include apple across macos, ios, ipados, watchos. Scope summary: macOS Big Sur prior to 11.0.1, macOS Catalina prior to 10.15.7, iOS/iPadOS prior to 14.2, iOS prior to 12.4.9, and watchOS prior to 7.1/6.2.9/5.3.9
Q3. What temporary mitigations or workarounds exist for CVE-2020-27950 before patching?
[Mitigation] Apply the official security updates provided by Apple to upgrade the operating system to the latest patched version Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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