How to Fix CVE-2020-27930: Out-of-bounds write in Apple iOS and iPadOS

WARNING: This vulnerability is on the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03). Federal civilian agencies must remediate by 2022-05-03. Treat it as active exploitation, not theoretical.

What is CVE-2020-27930?

A memory corruption issue was addressed with improved input validation. 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. Processing a maliciously crafted font may lead to arbitrary code execution.

Am I affected?

Run the version check that matches your platform:

# macOS
sw_vers
brew list --versions ios 2>/dev/null

Compare what you see against the Affected row above (Apple watchOS; Apple iOS and iPadOS; Apple macOS). If your build sits inside that range, you are exposed and should patch.

How to fix CVE-2020-27930

The primary fix is to upgrade Apple iOS and iPadOS to the patched build. Use the commands for your platform below; the patched version listed in the vendor advisory is: See vendor advisory.

macOS

# System updates (Apple-issued patches)
softwareupdate --list
sudo softwareupdate --install --all --restart

# For third-party tools managed by Homebrew
brew update
brew upgrade

Complete macOS / iOS remediation script

#!/usr/bin/env bash
# CVE-2020-27930 fix script for iOS and iPadOS
# Run on each affected Mac. iOS / iPadOS / watchOS / tvOS devices update via Settings.

set -euo pipefail
LOG="$HOME/Library/Logs/cve-2020-27930-fix-$(date +%Y%m%d-%H%M%S).log"
exec > >(tee -a "$LOG") 2>&1

echo "[1/4] Current OS version"
sw_vers

echo "[2/4] Listing available Apple updates"
softwareupdate --list || true

echo "[3/4] Installing all pending Apple security updates"
sudo softwareupdate --install --all --restart

echo "[4/4] Verifying"
sw_vers
echo "For iPhone / iPad: Settings -> General -> Software Update."
echo "For Apple Watch:   Watch app -> General -> Software Update."
echo "For Apple TV:      Settings -> System -> Software Updates -> Update Software."

If you can't patch immediately

If you cannot apply the patched version today, restrict exposure with one of the following runnable controls. None replace the patch.

Service-level fallback

# If the affected feature is optional, stop the service until the patch is applied
sudo systemctl stop ios
sudo systemctl disable ios

How to verify the fix worked

# Linux
ios --version 2>/dev/null || dpkg -s ios | grep -i version
rpm -q ios 2>/dev/null || true

# Windows
winget list | findstr /I "ios"
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above the patched build documented in the advisory. Restart any services that loaded the old library (systemctl restart <service> on Linux, restart the Windows service or reboot when prompted). For network appliances, run show version on the device and confirm the build matches the patched release.

Frequently asked questions

Related fixes

Other vulnerabilities in the same area that are worth patching alongside this one:

• How to Fix CVE-2020-9907: Out-of-bounds Write in Ios — Out-of-bounds Write in Ios
• How to Fix CVE-2020-9934: Security Vulnerability in Ios — Security Vulnerability in Ios
• How to Fix CVE-2020-9819: Out-of-bounds write in iOS , Out-of-bounds write in iOS
• How to Fix CVE-2020-27950: Initialization in Apple iOS and iPadOS , Initialization in Apple iOS and iPadOS
• How to Fix CVE-2020-3837: Out-of-bounds Write in Ios , Out-of-bounds Write in Ios

Is CVE-2020-27930 actually being exploited?

According to the data sources above, yes, CISA has it listed as actively exploited. Either way, the fix is the same: apply the vendor patch.

Do I need to reboot after patching?

For OS or kernel updates, yes. For most userland packages a systemctl restart <service> is enough. Any process that loaded the old shared library keeps using it until restarted, so when in doubt, reboot.

What is the CVSS score?

7.8 (high). Refer to the vendor advisory for the exact vector string.

Where is the official advisory?

See the References section at the bottom of this page; the vendor's URL is the authoritative source for affected builds and patched versions.

References

• Official vendor advisory: https://support.apple.com/en-us/HT211931
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-27930
• CISA KEV catalog entry: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• https://support.apple.com/en-us/HT211928
• https://support.apple.com/en-us/HT211929
• https://support.apple.com/en-us/HT211940
• https://support.apple.com/en-us/HT211944

*Written by Sai Kiran Pandrala. Assembled from the official vendor advisory, NVD record, and CISA KEV listing on 2026-05-25. Always confirm against the vendor's advisory before applying changes in production.*