CVE-2026-43666: An out-of-bounds write issue was addressed with improved bounds checking
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Routine
MEDIUM 6.2UPGRADEUPGRADEUPGRADE
CVE-2026-43666 is a medium-severity flaw (CVSS 6.2) affecting ipados, iphone os, macos. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
An out-of-bounds write issue was addressed with improved bounds checking. This issue is fixed in iOS 18.7.9 and iPadOS 18.7.9, iOS 26.5 and iPadOS 26.5, macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, macOS Tahoe 26.5, tvOS 26.5, visionOS 26.5, watchOS 26.5. An attacker on the local network may be able to cause a denial-of-service.
Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score
Am I affected?
Timeline
Published CVE record published
Updated Record last modified
apple ipados UPGRADE
Affected: < 18.7.9 · >= 26.0 and < 26.5
Fixed in: 18.7.9, 26.5
Safe to downgrade to: a release before 26.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
apple iphone os UPGRADE
Affected: < 18.7.9 · >= 26.0 and < 26.5
Fixed in: 18.7.9, 26.5
Safe to downgrade to: a release before 26.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
apple macos UPGRADE
Affected: >= 14.0 and < 14.8.7 · >= 15.0 and < 15.7.7 · >= 26.0 and < 26.5
Fixed in: 14.8.7, 15.7.7, 26.5
Safe to downgrade to: a release before 14.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
apple tvos UPGRADE
Affected: < 26.5
Fixed in: 26.5
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
apple visionos UPGRADE
Affected: < 26.5
Fixed in: 26.5
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
apple watchos UPGRADE
Affected: < 26.5
Fixed in: 26.5
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Verify at the official sourceNVD · CVE Program · Report a problem with this page Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2026-43666?
ipados: upgrade to 18.7.9, 26.5; iphone os: upgrade to 18.7.9, 26.5; macos: upgrade to 14.8.7, 15.7.7, 26.5. Exact commands for each OS are on this page.
Is CVE-2026-43666 being exploited?
CVE-2026-43666 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2026-43666 affect?
CVE-2026-43666 affects ipados, iphone os, macos. Severity is medium (CVSS 6.2). An out-of-bounds write issue was addressed with improved bounds checking. This issue is fixed in iOS 18.7.9 and iPadOS 18.7.9, iOS 26.5 and iPadOS 26.5, macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, macOS Tahoe 26.5, tvOS 26.5, visionOS 26.5,
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