DaystoPatch

MicrosoftExploited incident

Microsoft SharePoint Weak Authentication Vulnerability

CVE-2026-55040Critical, CVSS 9.1In CISA's Known Exploited Vulnerabilities catalog since 18 Aug 2026

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 version
  • 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-2026-55040ClaimedQuote verified

    Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

    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:e956cb64ea59e49c…
    Used in metrics
    Yes
    Dispute this timestamp
    4 more sources for this moment
    Microsoft advisory CVE-2026-55040ClaimedQuote not found in archive14 Jul 2026

    Microsoft SharePoint Server Security Feature Bypass Vulnerability. Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

    The vendor's own disclosure.

    Source
    Microsoft advisory CVE-2026-55040 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
    sha256:13b0a4b33ecd72c7…
    Used in metrics
    No, kept for the record
    Dispute this timestamp
    Bluesky postClaimedQuote not checked yet14 Jul 2026, 14:05 UTC

    Microsoft patched a SharePoint authentication bypass (CVE-2026-55040) discovered by Rapid7 using agentic AI. The CVSS 5.3 rating masks a full RCE chain: why severity goes beyond the score.

    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 yet14 Jul 2026, 23:26 UTC

    On-prem SharePoint: forge a valid session token from just a user's SID - no password, no clicks, straight to admin. 9 detections, 15 IOCs. Full analysis + IOCs: https://

    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
    CISA KEV (CVE-2026-55040)ClaimedQuote verified18 Aug 2026

    Microsoft SharePoint Weak Authentication Vulnerability

    Added to CISA's KEV catalog on 2026-08-18.

    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

  2. Vendor statement

    date onlysame dayUnverified: quote not found in the archived copy

    Microsoft advisory CVE-2026-55040ClaimedQuote not found in archive

    Microsoft SharePoint Server Security Feature Bypass Vulnerability. Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

    Source
    Microsoft advisory CVE-2026-55040 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
    sha256:13b0a4b33ecd72c7…
    Used in metrics
    Yes
    Dispute this timestamp

  3. First workaround

    No official mitigation found yet.

  4. First fix

    date onlysame day

    Microsoft advisory CVE-2026-55040ClaimedQuote verified

    Information published.

    Vendor Fix listed at the first revision

    Source
    Microsoft advisory CVE-2026-55040 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:e77540fbbdfa4c88…
    Used in metrics
    Yes
    Dispute this timestamp

  5. Fixed for all versions

    date onlysame day

    Microsoft advisory CVE-2026-55040ClaimedQuote verified

    Information published.

    every Known Affected product has a Vendor Fix and no later revision announces more updates

    Source
    Microsoft advisory CVE-2026-55040 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:e77540fbbdfa4c88…
    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

  • SharePoint
  • Microsoft SharePoint Enterprise Server 2016
  • Microsoft SharePoint Server 2019
  • Microsoft SharePoint Server Subscription Edition

Related

Microsoft report card