CVE-2026-78519: Use of uninitialized resource in Microsoft Office Outlook allows an unauthorized attacker to execute code over

This month

HIGH 8.8WATCHLISTMITIGATEMITIGATEMITIGATE

CVE-2026-78519 is a high-severity flaw (CVSS 8.8) 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.

Use of uninitialized resource in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

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	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.8% (top 43%)
CISA exploited list	No
Weakness	CWE-908
Published	2026-09-08
Last modified	2026-09-09

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-09-09 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-08 18:20 UTCPublished CVE record published
2026-09-09 18:58 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 outlook DOWNGRADE

Affected: 2016

Fixed in: no fixed release known

Safe to downgrade to: a release before 2016

1. Check installed version

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

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

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

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

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

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-2026-78519?

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-2026-78519 being exploited?

CVE-2026-78519 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-2026-78519 affect?

CVE-2026-78519 affects 365 apps, office 2019, office 2021. Severity is high (CVSS 8.8). Use of uninitialized resource in Microsoft Office Outlook allows an unauthorized attacker to execute code over a network.

How urgent is CVE-2026-78519?

Priority 50/100. High severity; On your watchlist

Software pages

Microsoft Office vulnerabilities · Outlook 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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