CVE-2026-40420: Use after free in Microsoft Office allows an authorized attacker to elevate privileges locally.

Routine

HIGH 8.8WATCHLISTMITIGATEDOWNGRADEDOWNGRADE

CVE-2026-40420 is a high-severity flaw (CVSS 8.8) affecting 365 apps, office, office long term servicing channel. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Use after free in Microsoft Office allows an authorized attacker to elevate privileges locally.

Why this priority

High severity
On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	8.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 89%)
CISA exploited list	No
Weakness	CWE-284
Published	2026-05-12
Last modified	2026-10-26

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-12 18:17 UTCPublished CVE record published
2026-10-26 18:10 UTCUpdated Record last modified

microsoft 365 apps MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy 365-apps || rpm -q 365-apps || 365-apps --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

microsoft office DOWNGRADE

Affected: 2019

Fixed in: no fixed release known

Safe to downgrade to: a release before 2019

1. Check installed version

apt-cache policy office || rpm -q office || office --version

2. No fixed release: DOWNGRADE to a release before 2019 (Debian / Ubuntu)

apt-cache madison office sudo apt install office=<VERSION_BEFORE_2019> sudo apt-mark hold office

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list office sudo dnf downgrade office-<VERSION_BEFORE_2019> sudo dnf versionlock add office

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

microsoft office long term servicing channel DOWNGRADE

Affected: 2021 · 2024

Fixed in: no fixed release known

Safe to downgrade to: a release before 2021

1. Check installed version

apt-cache policy office-long-term-servicing-channel || rpm -q office-long-term-servicing-channel || office-long-term-servicing-channel --version

2. No fixed release: DOWNGRADE to a release before 2021 (Debian / Ubuntu)

apt-cache madison office-long-term-servicing-channel sudo apt install office-long-term-servicing-channel=<VERSION_BEFORE_2021> sudo apt-mark hold office-long-term-servicing-channel

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list office-long-term-servicing-channel sudo dnf downgrade office-long-term-servicing-channel-<VERSION_BEFORE_2021> sudo dnf versionlock add office-long-term-servicing-channel

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · 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-2026-40420?

365 apps: mitigate or apply the listed mitigation; office: downgrade or apply the listed mitigation; office long term servicing channel: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-40420 being exploited?

CVE-2026-40420 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-2026-40420 affect?

CVE-2026-40420 affects 365 apps, office, office long term servicing channel. Severity is high (CVSS 8.8). Use after free in Microsoft Office allows an authorized attacker to elevate privileges locally.

How urgent is CVE-2026-40420?

Priority 39/100. High severity; On your watchlist

Software pages

Microsoft Office vulnerabilities

Related CVEs

CVE-2026-23657 HIGH 7.8 MITIGATE DOWNGRADE Use after free in Microsoft Office Word allows an unauthorized attacker to execute code locally.
CVE-2026-32190 HIGH 8.4 MITIGATE DOWNGRADE Use after free in Microsoft Office allows an unauthorized attacker to execute code locally.
CVE-2026-32189 HIGH 7.8 MITIGATE DOWNGRADE Use after free in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
CVE-2026-32188 HIGH 7.1 MITIGATE DOWNGRADE Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.
CVE-2026-32200 HIGH 7.8 MITIGATE DOWNGRADE Use after free in Microsoft Office PowerPoint allows an unauthorized attacker to execute code locally.

References

← Back to latest CVEs