DaystoPatch

MicrosoftExploited incident

Microsoft Office Security Feature Bypass Vulnerability

CVE-2026-21509High, CVSS 7.8In CISA's Known Exploited Vulnerabilities catalog since 26 Jan 2026

  • Exploited before a fix

Automated timeline. Not yet checked by a researcher, so it doesn't count toward any grade.

FixedFixed for every supported version on the day it became public.

Response

Silence
same day
First public report to first vendor statementUnverified source
Exposure
same day
First public report to first fix
Follow-through
same day
First public report to a fix for every supported versionUnverified source
  • Vendor silent
  • Vendor statement, no fix
  • Fixed for some versions
  • Fixed when disclosed
  • Date only, no time of day

Timeline and evidence

Open a moment to see its source and archived quote.

  1. First public report

    CVE.org record CVE-2026-21509ClaimedQuote verified

    Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

    CVE record published.

    Recorded time
    Precision
    To the minute
    Origin
    Claimed. The date the source gives.
    Quote check
    Found in the archived copy
    Snapshot
    sha256:60952fdccb97748c…
    Used in metrics
    Yes
    Dispute this timestamp
    5 more sources for this moment
    Microsoft advisory CVE-2026-21509ClaimedQuote not found in archive26 Jan 2026

    Microsoft Office Security Feature Bypass Vulnerability. Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

    The vendor's own disclosure.

    Source
    Microsoft advisory CVE-2026-21509 vendor advisory
    Recorded time
    Precision
    Date only (no time of day is shown)
    Origin
    Claimed. The date the source gives.
    Quote check
    Not found in the archived copy. Treat with caution.
    Snapshot
    sha256:223eb29818278cd0…
    Used in metrics
    No, kept for the record
    Dispute this timestamp
    CISA KEV (CVE-2026-21509)ClaimedQuote verified26 Jan 2026

    Microsoft Office Security Feature Bypass Vulnerability

    Added to CISA's KEV catalog on 2026-01-26.

    Recorded time
    Precision
    Date only (no time of day is shown)
    Origin
    Claimed. The date the source gives.
    Quote check
    Found in the archived copy
    Snapshot
    sha256:ef8fffede5c47200…
    Used in metrics
    No, kept for the record
    Dispute this timestamp
    Bluesky postClaimedQuote not checked yet26 Jan 2026, 17:40 UTC

    Wow - Office security feature bypass patched OOB after active exploitation detected. Path now - CVE-2026-21509. At least the Preview Pane isn't an attack vector. msrc.microsoft.com/update-guide...

    Earliest third-party post we hold.

    Source
    Bluesky post social
    Recorded time
    Precision
    To the minute
    Origin
    Claimed. The date the source gives.
    Quote check
    Not checked yet
    Snapshot
    No archived snapshot
    Used in metrics
    No, kept for the record
    Dispute this timestamp
    Mastodon postClaimedQuote not checked yet27 Jan 2026, 06:13 UTC

    Microsoft łata lukę zero-day w Office – bezpieczeństwo znów zagrożone Kto jeszcze wierzy, że w 2026 otwieranie dokumentu to czynność bezpieczna jak herbata w biurze? Microsoft właśnie załatał świeżo

    Earliest third-party post we hold.

    Source
    Mastodon post social
    Recorded time
    Precision
    To the minute
    Origin
    Claimed. The date the source gives.
    Quote check
    Not checked yet
    Snapshot
    No archived snapshot
    Used in metrics
    No, kept for the record
    Dispute this timestamp
    Hacker NewsClaimedQuote not checked yet2 Feb 2026, 06:44 UTC

    Title: Just patched CVE-2026-21509? Here's why you're still exposed

    Earliest third-party post we hold. An independent author on another platform posted within 48 hours. Used for unreviewed incidents only, never graded.

    Source
    Hacker News hn
    Recorded time
    Precision
    To the minute
    Origin
    Claimed. The date the source gives.
    Quote check
    Not checked yet
    Snapshot
    No archived snapshot
    Used in metrics
    No, kept for the record
    Dispute this timestamp

  2. Vendor statement

    date onlysame dayUnverified: quote not found in the archived copy

    Microsoft advisory CVE-2026-21509ClaimedQuote not found in archive

    Microsoft Office Security Feature Bypass Vulnerability. Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

    Source
    Microsoft advisory CVE-2026-21509 vendor advisory
    Recorded time
    Precision
    Date only (no time of day is shown)
    Origin
    Claimed. The date the source gives.
    Quote check
    Not found in the archived copy. Treat with caution.
    Snapshot
    sha256:223eb29818278cd0…
    Used in metrics
    Yes
    Dispute this timestamp

  3. First workaround

    date onlysame day

    Microsoft advisory CVE-2026-21509ClaimedQuote verified

    The following revisions have been made: 1) Microsoft is announcing the availability of the security updates for Microsoft Office 2016 and 2019.

    Workaround/Mitigation remediation listed

    Source
    Microsoft advisory CVE-2026-21509 vendor advisory
    Recorded time
    Precision
    Date only (no time of day is shown)
    Origin
    Claimed. The date the source gives.
    Quote check
    Found in the archived copy
    Snapshot
    sha256:e5f3b20c3de7f65d…
    Used in metrics
    Yes
    Dispute this timestamp

  4. First fix

    date onlysame day

    Microsoft advisory CVE-2026-21509ClaimedQuote verified

    The following revisions have been made: 1) Microsoft is announcing the availability of the security updates for Microsoft Office 2016 and 2019.

    revision 2.0

    Source
    Microsoft advisory CVE-2026-21509 vendor advisory
    Recorded time
    Precision
    Date only (no time of day is shown)
    Origin
    Claimed. The date the source gives.
    Quote check
    Found in the archived copy
    Snapshot
    sha256:e5f3b20c3de7f65d…
    Used in metrics
    Yes
    Dispute this timestamp

  5. Fixed for all versions

    date onlysame dayUnverified: derived by rule, not read from a source

    Microsoft advisory CVE-2026-21509Inferred

    Microsoft Office Security Feature Bypass Vulnerability. Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

    Patch-day rule: Microsoft ships fixes in the advisory that discloses a bug, and this advisory states that fixed versions exist. So the vendor statement, first fix and fix for all versions all take the advisory's publication time.

    Source
    Microsoft advisory CVE-2026-21509 vendor advisory
    Recorded time
    Precision
    Date only (no time of day is shown)
    Origin
    Inferred. Derived by a documented rule.
    Quote check
    Not found in the archived copy. Treat with caution.
    Snapshot
    sha256:223eb29818278cd0…
    Used in metrics
    Yes
    Dispute this timestamp

Send this to your boss

No brief for this incident yet. We write one for every open incident and every critical bug exploited before a fix.

Affected products

  • Office
  • Microsoft 365 Apps for Enterprise for 32-bit Systems
  • Microsoft 365 Apps for Enterprise for 64-bit Systems
  • Microsoft Office 2016 (32-bit edition)
  • Microsoft Office 2016 (64-bit edition)
  • Microsoft Office 2019 for 32-bit editions
  • Microsoft Office 2019 for 64-bit editions
  • Microsoft Office LTSC 2021 for 32-bit editions
  • Microsoft Office LTSC 2021 for 64-bit editions
  • Microsoft Office LTSC 2024 for 32-bit editions
  • Microsoft Office LTSC 2024 for 64-bit editions

Related

Microsoft report card