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Response snapshot Oct 27, 2026, 00:53 UTC

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VulnerabilityCVE-2025-53770Known exploitation

On-premises SharePoint untrusted deserialization

Untrusted deserialization permits remote code execution in affected on-premises SharePoint Server deployments. CISA lists known exploitation, and Microsoft documents related attack chains, stolen machine keys, and ransomware deployment.

At a glance

Exploited
Yes: on CISA's Known Exploited list
Severity
9.8 Critical (CVSS 3.1)
Chance of exploitation
100.0% in the next 30 days
CISA federal deadline
Jul 21, 2025: passed
Sources
3 independent sources

What to do

Apply Microsoft's applicable SharePoint updates, enable and correctly configure AMSI, rotate ASP.NET machine keys, restart IIS, and perform incident response. Use the vendor's full guidance for prerequisites and compromise assessment.

CISA's required action: Disconnect public-facing versions of SharePoint Server that have reached their end-of-life (EOL) or end-of-service (EOS) to include SharePoint Server 2013 and earlier versions. For supported versions, please follow the mitigations according to CISA (URL listed below in Notes) and vendor instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services or discontinue use of the product if mitigations are not available.

Read Microsoft Threat Intelligence SharePoint investigation (opens a new tab)

CISA federal deadline

Federal due date passed

Applies to covered US federal agencies; it is not your organization's deadline.

Added to the catalog Known ransomware use: Known
CISA catalog (opens a new tab)

Scores and how they were measured

CVSS base severity

9.8

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:F/RL:W/RC:C

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

100.0%

Scored Percentile 100.0%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    Microsoft Threat Intelligence SharePoint investigation (opens a new tab)

    Observed related exploitation, SharePoint Online exclusion, machine-key theft, ransomware, and updated recovery guidance.

    Published Checked

  2. Primary source

    CISA KEV JSON: CVE-2025-53770 (opens a new tab)

    This CVE's membership, patch-bypass relationship, addition date, federal due date, and required action.

    Published Checked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2025-53770, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

  4. Primary source

    CVE Program CNA microsoft (opens a new tab)

    The published CVE-2025-53770 document's CNA supplies this CVSS 3.1 base score, vector, and authoritative source update date.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2025, July 23). On-premises SharePoint untrusted deserialization (CVE-2025-53770). https://kevwire.com/record/CVE-2025-53770

MLA

"On-premises SharePoint untrusted deserialization (CVE-2025-53770)." KEVWire, 23 July 2025, kevwire.com/record/CVE-2025-53770.

Chicago

KEVWire. "On-premises SharePoint untrusted deserialization (CVE-2025-53770)." Last modified July 23, 2025. https://kevwire.com/record/CVE-2025-53770.

Evidence summary (plain text)

On-premises SharePoint untrusted deserialization (Jul 20, 2025).
Untrusted deserialization permits remote code execution in affected on-premises SharePoint Server deployments. CISA lists known exploitation, and Microsoft documents related attack chains, stolen machine keys, and ransomware deployment.
CVSS 9.8 (version 3.1; evidence as of Feb 13, 2026; https://cveawg.mitre.org/api/cve/CVE-2025-53770).
EPSS 100.0% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2025-53770&date=2026-10-26).
Sources:
Microsoft Threat Intelligence SharePoint investigation: https://www.microsoft.com/en-us/security/blog/2025/07/22/disrupting-active-exploitation-of-on-premises-sharepoint-vulnerabilities/
CISA KEV JSON: CVE-2025-53770: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2025-53770&date=2026-10-26
CVE Program CNA microsoft: https://cveawg.mitre.org/api/cve/CVE-2025-53770
Record ID: CVE-2025-53770.
Record origin: Editorial selection.
AI evidence: Not assessed.
Known exploitation: Documented by a cited source.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
CISA federal due date: Jul 21, 2025. This is a deadline for covered US federal agencies, not the reader's SLA.
About this data

This record was assembled editorially. Editorial review: Oct 26, 2026. Editorial selection does not make a reported claim independently confirmed.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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