---
title: "CVE-2025-53770: Microsoft SharePoint Deserialization of Untrusted Data Vulnerability"
url: https://erroneo.us/security/cve/CVE-2025-53770/
description: "CVE-2025-53770 (Microsoft SharePoint): Exploited in the wild (CISA KEV). Deserialization of untrusted data in on-premises Microsoft SharePoint Server allows…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-07-20
date_modified: 2026-10-21
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-53770"
kev: true
cvss: 9.8
epss: 0.99999
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-53770: Microsoft SharePoint Deserialization of Untrusted Data Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Microsoft SharePoint. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-07-20, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-07-21 ; treat that as the outer limit, not the target. CISA also lists it as known to be used in ransomware campaigns .
- EPSS 100.0% , percentile 100.0: FIRST’s model estimates a 100.0% chance of exploitation activity in the next 30 days, higher than 100.0% of all scored CVEs (very high). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Check exposure. ToolShell: SharePoint On-Prem Unauthenticated RCE Chain — Fixes shipped in July 2025, but ToolShell stole ASP.NET machine keys that survive patching, so any on-prem SharePoint that was internet-facing then needs proof that keys were rotated and no backdoor remains.

## What it is

Deserialization of untrusted data in on-premises Microsoft SharePoint Server allows an unauthorized attacker to execute code over a network. Microsoft is aware that an exploit for CVE-2025-53770 exists in the wild. Microsoft is preparing and fully testing a comprehensive update to address this vulnerability. In the meantime, please make sure that the mitigation provided in this CVE documentation is in place so that you are protected from exploitation.

## Affected products (CVE record)

- Microsoft Microsoft SharePoint Enterprise Server 2016: 16.0.0 < 16.0.5513.1001
- Microsoft Microsoft SharePoint Server 2019: 16.0.0 < 16.0.10417.20037
- Microsoft Microsoft SharePoint Server Subscription Edition: 16.0.0 < 16.0.18526.20508

## Severity

- microsoft CVSS 3.1: 9.8 `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`

## Exploitation

- CISA KEV: added 2025-07-20; federal due date 2025-07-21. Known ransomware use: Known.
- CISA 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.
- CISA SSVC assessment: exploitation active , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 100.00% probability of exploitation activity in the next 30 days; percentile 100.0.

## Sources

- [Microsoft SharePoint Server Remote Code Execution Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-53770)
- [Listed in CISA KEV notes (microsoft.com)](https://www.microsoft.com/en-us/security/blog/2025/07/22/disrupting-active-exploitation-of-on-premises-sharepoint-vulnerabilities/)
- [CVE.org record CVE-2025-53770](https://www.cve.org/CVERecord?id=CVE-2025-53770)
- [NVD entry CVE-2025-53770](https://nvd.nist.gov/vuln/detail/CVE-2025-53770)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-53770)
- [Listed in CISA KEV notes (cisa.gov)](https://www.cisa.gov/news-events/alerts/2025/07/20/microsoft-releases-guidance-exploitation-sharepoint-vulnerability-cve-2025-53770)
- [msrc.microsoft.com](https://msrc.microsoft.com/blog/2025/07/customer-guidance-for-sharepoint-vulnerability-cve-2025-53770/)
- [research.eye.security](https://research.eye.security/sharepoint-under-siege/)
- [bleepingcomputer.com](https://www.bleepingcomputer.com/news/microsoft/microsoft-sharepoint-zero-day-exploited-in-rce-attacks-no-patch-available/)
- [forbes.com](https://www.forbes.com/sites/daveywinder/2025/07/20/microsoft-confirms-ongoing-mass-sharepoint-attack---no-patch-available/)
- [x.com](https://x.com/Shadowserver/status/1946900837306868163)
- [github.com](https://github.com/kaizensecurity/CVE-2025-53770)
- [therecord.media](https://therecord.media/microsoft-sharepoint-zero-day-vulnerability-exploited-globally)
- [news.ycombinator.com](https://news.ycombinator.com/item?id=44629710)
- [arstechnica.com](https://arstechnica.com/security/2025/07/sharepoint-vulnerability-with-9-8-severity-rating-is-under-exploit-across-the-globe/)
- [darkreading.com](https://www.darkreading.com/remote-workforce/microsoft-rushes-emergency-fix-exploited-sharepoint-toolshell-flaw)

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Source page: https://erroneo.us/security/cve/CVE-2025-53770/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt