DaystoPatch

MicrosoftExploited incident

Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability

CVE-2023-21529High, CVSS 8.8In CISA's Known Exploited Vulnerabilities catalog since 13 Apr 2026

  • Known ransomware use

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

UnknownNo evidence of the current fix status.

Response

Silence
not dated
First public report to first vendor statement
Exposure
not dated
First public report to first fix
Follow-through
not dated
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-2023-21529ClaimedQuote verified

    Microsoft Exchange Server Remote Code Execution Vulnerability

    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:d1afe221d252080b…
    Used in metrics
    Yes
    Dispute this timestamp
    3 more sources for this moment
    Mastodon postClaimedQuote not checked yet14 Feb 2023, 21:20 UTC

    Microsoft Patch Tuesday, February 2023 Edition https:// krebsonsecurity.com/2023/02/mi crosoft-patch-tuesday-february-2023-edition/ # MicrosoftPatchTuesdayFebruary2023 # TrendMicroZeroDayInitiative

    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
    Bluesky postClaimedQuote not checked yet5 Sep 2024, 19:05 UTC

    Piotr Bazydło details his research into exploiting #Microsoft #Exchange after ProxyNotShell was patched. Today's post covers CVE-2023-21529: abuse of the allowed MultiValuedProperty class for RCE. Check it out: www.zerodayinitiative.com/blog/2024/9/...

    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
    CISA KEV (CVE-2023-21529)ClaimedQuote verified13 Apr 2026

    Microsoft Exchange Server Deserialization of Untrusted Data Vulnerability

    Added to CISA's KEV catalog on 2026-04-13.

    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

    No public statement from the vendor found yet.

  3. First workaround

    No official mitigation found yet.

  4. First fix

    No fixed release found yet for any affected branch.

  5. Fixed for all versions

    No evidence yet of fixed releases for every supported branch.

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

  • Exchange Server

Related

No related incidents.

Microsoft report card