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

Should you act?

Exploited: patch now if you run it

CISA has confirmed exploitation in the wild. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• 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.

CISA’s summary

Microsoft SharePoint Server on-premises contains a deserialization of untrusted data vulnerability that could allow an unauthorized attacker to execute code over a network. This vulnerability could be chained with CVE-2025-53771. CVE-2025-53770 is a patch bypass for CVE-2025-49704, and the updates for CVE-2025-53770 include more robust protection than those for CVE-2025-49704.

Weakness type: CWE-502.

Product: Microsoft SharePoint · Assigned by: microsoft · Published: 2025-07-20

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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.

Timeline

• 2025-07-19 — erroneo.us brief: ToolShell: SharePoint On-Prem Unauthenticated RCE Chain
• 2025-07-20 — Added to CISA’s Known Exploited Vulnerabilities catalog
• 2025-07-20 — CVE record published by microsoft
• 2025-07-21 — CISA remediation deadline for US federal agencies
• 2026-08-04 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Microsoft SharePoint Server Remote Code Execution Vulnerability msrc.microsoft.com
2. Listed in CISA KEV notes (microsoft.com) microsoft.com

Vulnerability records

1. CVE.org record CVE-2025-53770 cve.org
2. NVD entry CVE-2025-53770 nvd.nist.gov

Government

1. CISA Known Exploited Vulnerabilities catalog entry cisa.gov
2. Listed in CISA KEV notes (cisa.gov) cisa.gov

Other references from the CVE record and advisory

1. msrc.microsoft.com msrc.microsoft.com
2. research.eye.security research.eye.security
3. bleepingcomputer.com bleepingcomputer.com
4. forbes.com forbes.com
5. x.com x.com
6. github.com github.com
7. therecord.media therecord.media
8. news.ycombinator.com news.ycombinator.com
9. arstechnica.com arstechnica.com
10. darkreading.com darkreading.com

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