CVE-2021-28474Public exploitNetwork attack vector

Authenticated code execution via control interpretation conflict

Published May 11, 2021 · Updated Aug 3, 2024

Remote code execution in Microsoft SharePoint Server allows remote authenticated users to run arbitrary code through crafted page markup. EditingPageParser verifies the runat attribute before HTML decoding, but processing decodes it and instantiates a server-side control that the safety check skipped. Exploitation requires ManageLists permission and executes code under the SharePoint web application service account.

CVSS severity8.8
High
EPSS probability50.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Remote code execution in Microsoft SharePoint Server allows remote authenticated users to run arbitrary code through crafted page markup. EditingPageParser verifies the runat attribute before HTML decoding, but processing decodes it and instantiates a server-side control that the safety check skipped. Exploitation requires ManageLists permission and executes code under the SharePoint web application service account.

The record

CVE
CVE-2021-28474
Published
May 11, 2021
Updated
Aug 3, 2024
Vendor
Microsoft
Product
Microsoft SharePoint Foundation 2013
Classifications
CWE-436, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 11, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=15.0.0 <15.0.5345.1000

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · Microsoft SharePoint Foundation 2013version=15.0.0 <15.0.5345.1000
Microsoft · Microsoft SharePoint Enterprise Server 2016version=16.0.0 <16.0.5161.1000
Microsoft · Microsoft SharePoint Server 2019version=16.0.0 <16.0.10374.20000

Published CVSS scores

8.8Microsoft CorporationCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.5NIST National Vulnerability DatabaseAV:N/AC:L/Au:S/C:P/I:P/A:P
8.8NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-436Interpretation Conflict
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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