PatchTheCVECVE-2026-40358: Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.
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This month
HIGH 8.4WATCHLISTMITIGATEDOWNGRADEDOWNGRADE
CVE-2026-40358 is a high-severity flaw (CVSS 8.4) 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.
Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.
Why this priority
- High severity
- On your watchlist
No fix is published yet: follow the downgrade or mitigation steps.
Risk facts
| CVSS score | 8.4 (High) |
| Attack vector | Local |
| Attack complexity | Low |
| Privileges needed | None |
| User interaction | None |
| EPSS exploit chance | 0.4% (top 69%) |
| 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 office DOWNGRADE
Affected: 2016 · 2019
Fixed in: no fixed release known
Safe to downgrade to: a release before 2016
1. Check installed version
apt-cache policy office || rpm -q office || office --version
2. No fixed release: DOWNGRADE to a release before 2016 (Debian / Ubuntu)
apt-cache madison office
sudo apt install office=<VERSION_BEFORE_2016>
sudo apt-mark hold office
2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)
dnf --showduplicates list office
sudo dnf downgrade office-<VERSION_BEFORE_2016>
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.
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-2026-40358?
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-2026-40358 being exploited?
CVE-2026-40358 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-2026-40358 affect?
CVE-2026-40358 affects 365 apps, office, office long term servicing channel. Severity is high (CVSS 8.4). Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code locally.
How urgent is CVE-2026-40358?
Priority 42/100. High severity; On your watchlist
Software pages
Microsoft Office vulnerabilities
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