CVE-2026-66806: Off-by-one error in Microsoft Office Word allows an unauthorized attacker to disclose information locally.

Routine

MEDIUM 5.5WATCHLISTMITIGATEMITIGATEMITIGATE

CVE-2026-66806 is a medium-severity flaw (CVSS 5.5) affecting 365 apps, office 2019, office 2021. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Off-by-one error in Microsoft Office Word allows an unauthorized attacker to disclose information locally.

Why this priority

On your watchlist

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

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-125, CWE-193
Published	2026-08-11
Last modified	2026-08-14

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-08-14 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-11 17:19 UTCPublished CVE record published
2026-08-14 13:06 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 2019 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 office-2019 || rpm -q office-2019 || office-2019 --version

No fixed or unaffected release known

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

microsoft office 2021 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 office-2021 || rpm -q office-2021 || office-2021 --version

No fixed or unaffected release known

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

microsoft office 2024 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 office-2024 || rpm -q office-2024 || office-2024 --version

No fixed or unaffected release known

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

microsoft word DOWNGRADE

Affected: 2016

Fixed in: no fixed release known

Safe to downgrade to: a release before 2016

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 2016 (Debian / Ubuntu)

apt-cache madison word sudo apt install word=<VERSION_BEFORE_2016> sudo apt-mark hold word

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

dnf --showduplicates list word sudo dnf downgrade word-<VERSION_BEFORE_2016> sudo dnf versionlock add word

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-2026-66806?

365 apps: mitigate or apply the listed mitigation; office 2019: mitigate or apply the listed mitigation; office 2021: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-66806 being exploited?

CVE-2026-66806 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-2026-66806 affect?

CVE-2026-66806 affects 365 apps, office 2019, office 2021. Severity is medium (CVSS 5.5). Off-by-one error in Microsoft Office Word allows an unauthorized attacker to disclose information locally.

How urgent is CVE-2026-66806?

Priority 34/100. 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

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