Atomicorp WAF Research Note: CVE-2025-53770

Microsoft SharePoint Server - Remote Code Execution (ToolShell)

CVE Details

• Already protected by existing Atomicorp WAF rules
• Protection status: Understanding Atomicorp WAF Protection Status
• CVE: CVE-2025-53770
• Name: Microsoft SharePoint Server - Remote Code Execution (ToolShell)
• Severity: Critical
• CVSS: 9.8 (v3.1) (Critical)
• CVSS version: 3.1
• CVSS source: microsoft CNA
• CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • Attack vector: Network
  • Attack complexity: Low
  • Privileges required: None
  • User interaction: None
  • Scope: Unchanged
  • Confidentiality impact: High
  • Integrity impact: High
  • Availability impact: High
• CWE: CWE-502 — Deserialization of Untrusted Data
• Related CAPEC attack patterns (via MITRE CWE relationships): CAPEC-586 (opens in a new tab)
• Vendor: microsoft
• Vulnerable product: sharepoint server
• CVE published: 2025-07-20
• CVE last modified: 2026-08-04
• Affected versions (NVD configurations):
  • sharepoint server: < 16.0.18526.20508
  • sharepoint server: 2016
  • sharepoint server: 2019
• EPSS: 1.0000; 100.0th percentile (FIRST (opens in a new tab) )
• CISA KEV: Listed (added 2025-07-20)
  • Known ransomware campaign use: Known
• Latest Update: 2026-09-06
• Selected Rule IDs observed: 330906 , 350147 , 398001
• Matching rules: 3; rules with blocking actions: 2
• Would-block Rule IDs: 330906 , 350147
• Request surfaces inspected: JSON request data, Request URI, Request argument names, Request arguments, SOAP request data

Vulnerability Description

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.

Recommended Actions

1. Maintain the observed Atomicorp protections. Keep your Atomicorp commercial rules current and confirm that the selected observed rules (330906 , 350147 ) have not been locally disabled. Atomicorp commercial rules are enabled by default. If you use Atomic WAF, review the applicable policy and rule settings.

2. Apply the vendor’s remediation. WAF protection is defense in depth and does not replace upgrading or following the affected vendor’s guidance.

   • Affected versions: Microsoft Microsoft SharePoint Enterprise Server 2016 versions earlier than 16.0.5513.1001.
   • Affected versions: Microsoft Microsoft SharePoint Server 2019 versions earlier than 16.0.10417.20037.
   • Affected versions: Microsoft Microsoft SharePoint Server Subscription Edition versions earlier than 16.0.18526.20508.
   • The CVE record does not include written upgrade or workaround instructions, but it does publish the following patch or mitigation reference:
     • Patch or mitigation information (opens in a new tab)
     • Patch or mitigation information (opens in a new tab)
   • CISA KEV 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 KEV federal remediation due date: 2025-07-21

3. Validate after changes. Confirm rule updates are current, review WAF events for the affected application, and test application behavior after vendor upgrades, mitigations, or local policy changes.

Research Notes

Atomicorp WAF protections are designed around attack techniques and exploit behaviors, allowing existing protections to apply across multiple vulnerabilities without requiring a unique rule for every CVE.

Public Vulnerability References

• NVD (opens in a new tab)
• CVE Record (opens in a new tab)
• Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-53770 (opens in a new tab)
• Exploit or technical research: https://arstechnica.com/security/2025/07/sharepoint-vulnerability-with-9-8-severity-rating-is-under-exploit-across-the-globe/ (opens in a new tab)
• Exploit or technical research: https://github.com/kaizensecurity/CVE-2025-53770 (opens in a new tab)
• Vendor advisory: https://msrc.microsoft.com/blog/2025/07/customer-guidance-for-sharepoint-vulnerability-cve-2025-53770/ (opens in a new tab)
• CVE authority reference: https://news.ycombinator.com/item?id=44629710 (opens in a new tab)
• Patch or mitigation: https://research.eye.security/sharepoint-under-siege/ (opens in a new tab)
• CVE authority reference: https://therecord.media/microsoft-sharepoint-zero-day-vulnerability-exploited-globally (opens in a new tab)
• CVE authority reference: https://www.bleepingcomputer.com/news/microsoft/microsoft-sharepoint-zero-day-exploited-in-rce-attacks-no-patch-available/ (opens in a new tab)
• Exploit or technical research: https://www.cisa.gov/news-events/alerts/2025/07/20/microsoft-releases-guidance-exploitation-sharepoint-vulnerability-cve-2025-53770 (opens in a new tab)
• CVE authority reference: https://www.darkreading.com/remote-workforce/microsoft-rushes-emergency-fix-exploited-sharepoint-toolshell-flaw (opens in a new tab)
• CVE authority reference: https://www.forbes.com/sites/daveywinder/2025/07/20/microsoft-confirms-ongoing-mass-sharepoint-attack—no-patch-available/ (opens in a new tab)
• Exploit or technical research: https://x.com/Shadowserver/status/1946900837306868163 (opens in a new tab)
• CVE authority reference: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-53770 (opens in a new tab)

Test or Research Source

• Source: http/cves/2025/CVE-2025-53770.yaml (opens in a new tab)
• Tags: cve, cve2025, kev, microsoft, rce, sharepoint, toolshell, vkev, vuln

Research Note Context

This research note documents exploit-technique analysis associated with this vulnerability and references Atomicorp WAF protections observed during engineering review, testing, or validation activities.

Atomicorp security controls are generally designed to identify and mitigate attack techniques and exploit behaviors rather than individual CVE identifiers. As a result, protections developed for one vulnerability may also apply to related attack variants and future vulnerabilities using similar techniques.

Learn More

Atomicorp develops commercially supported security technologies for web applications, servers, endpoints, workloads, and legacy enterprise platforms.

Organizations interested in protecting systems against exploit techniques associated with vulnerabilities such as this one can learn more about:

• Atomic ModSecurity Rules: commercially maintained WAF rules for ModSecurity deployments, including protections for web attacks, bots, scanners, malware, exploitation attempts, and emerging vulnerability classes.
• Atomic WAF: an enterprise web application firewall with Atomicorp rules, centralized management, reporting, authentication controls, and operational tooling.
• Atomic ModSecurity Integrator: a special licensing option for MSPs, MSSPs, OEMs, VARs, reverse proxy providers, and other integrators who want to incorporate Atomicorp ModSecurity rule technology into their own products or services.
• Atomic OSSEC: an enterprise OSSEC-based intrusion detection, compliance, and security monitoring platform.
• Atomic Protector: workload protection for Linux, web, cloud, data center, and hybrid environments.

For additional information, product evaluations, or technical discussions, visit https://www.atomicorp.com/ or https://modsecurity.io/ (opens in a new tab) .