CVE-2026-56178: Time-of-check time-of-use (toctou) race condition in Microsoft Defender for Endpoint allows an authorized atta

Routine

MEDIUM 5.5WATCHLISTUPGRADE

CVE-2026-56178 is a medium-severity flaw (CVSS 5.5) affecting defender for endpoint. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Time-of-check time-of-use (toctou) race condition in Microsoft Defender for Endpoint allows an authorized attacker to elevate privileges locally.

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	5.5 (Medium)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.2% (top 87%)
CISA exploited list	No
Weakness	CWE-367
Published	2026-07-14
Last modified	2026-10-24

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 18:18 UTCPublished CVE record published
2026-10-24 21:10 UTCUpdated Record last modified

microsoft defender for endpoint UPGRADE

Affected: >= 101.0.0 and < 101.26042.0020

Fixed in: 101.26042.0020

Safe to downgrade to: a release before 101.0.0

1. Check installed version

apt-cache policy defender-for-endpoint || rpm -q defender-for-endpoint || defender-for-endpoint --version

2. UPGRADE to 101.26042.0020 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade defender-for-endpoint

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade defender-for-endpoint

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 101.0.0 (Debian / Ubuntu)

apt-cache madison defender-for-endpoint sudo apt install defender-for-endpoint=<VERSION_BEFORE_101.0.0> sudo apt-mark hold defender-for-endpoint

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list defender-for-endpoint sudo dnf downgrade defender-for-endpoint-<VERSION_BEFORE_101.0.0> sudo dnf versionlock add defender-for-endpoint

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-2026-56178?

defender for endpoint: upgrade to 101.26042.0020. Exact commands for each OS are on this page.

Is CVE-2026-56178 being exploited?

CVE-2026-56178 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-2026-56178 affect?

CVE-2026-56178 affects defender for endpoint. Severity is medium (CVSS 5.5). Time-of-check time-of-use (toctou) race condition in Microsoft Defender for Endpoint allows an authorized attacker to elevate privileges locally.

How urgent is CVE-2026-56178?

Priority 28/100. On your watchlist

Software pages

Windows Defender vulnerabilities

Related CVEs

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CVE-2026-54123 MEDIUM 5.5 UPGRADE Exposure of sensitive information to an unauthorized actor in Microsoft Defender for Endpoint allows an author

References

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