PatchTheCVECVE-2026-40359: Use after free in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
39
Routine
HIGH 7.8WATCHLISTMITIGATEDOWNGRADEDOWNGRADE
CVE-2026-40359 is a high-severity flaw (CVSS 7.8) affecting 365 apps, excel, office. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
Use after free in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
Why this priority
- High severity
- On your watchlist
A fixed release or distro patch exists.
Risk facts
| CVSS score | 7.8 (High) |
| Attack vector | Local |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | Required |
| EPSS exploit chance | 0.3% (top 74%) |
| CISA exploited list | No |
| Weakness | CWE-416 |
| 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
- Published CVE record published
- Updated 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 excel DOWNGRADE
Affected: 2016
Fixed in: no fixed release known
Safe to downgrade to: a release before 2016
1. Check installed version
apt-cache policy excel || rpm -q excel || excel --version
2. No fixed release: DOWNGRADE to a release before 2016 (Debian / Ubuntu)
apt-cache madison excel
sudo apt install excel=<VERSION_BEFORE_2016>
sudo apt-mark hold excel
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list excel
sudo dnf downgrade excel-<VERSION_BEFORE_2016>
sudo dnf versionlock add excel
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 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.
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.
microsoft office online server UPGRADE
Affected: < 16.0.10417.20128
Fixed in: 16.0.10417.20128
Safe to downgrade to: no unaffected older release
1. Check installed version
apt-cache policy office-online-server || rpm -q office-online-server || office-online-server --version
2. UPGRADE to 16.0.10417.20128 (Debian / Ubuntu)
sudo apt update && sudo apt install --only-upgrade office-online-server
2. UPGRADE (RHEL / Amazon Linux / Fedora)
sudo dnf upgrade office-online-server
Note
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
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.
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-2026-40359?
365 apps: mitigate or apply the listed mitigation; excel: downgrade or apply the listed mitigation; office: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2026-40359 being exploited?
CVE-2026-40359 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-2026-40359 affect?
CVE-2026-40359 affects 365 apps, excel, office. Severity is high (CVSS 7.8). Use after free in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
How urgent is CVE-2026-40359?
Priority 39/100. High severity; On your watchlist
Software pages
Microsoft Office vulnerabilities
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