CVE-2021-42309Network attack vector

Authenticated code execution via nested unsafe control

Published Dec 15, 2021 · Updated Aug 4, 2024

Improper input validation in Microsoft SharePoint Server allows remote authenticated users to execute code through server-side controls. The control parser permits an unsafe server-side control to be specified as a child of a permitted control and then instantiates it. A valid SharePoint account is required, and successful exploitation runs code in the SharePoint service account context.

CVSS severity8.8
High
EPSS probability2.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Microsoft SharePoint Server allows remote authenticated users to execute code through server-side controls. The control parser permits an unsafe server-side control to be specified as a child of a permitted control and then instantiates it. A valid SharePoint account is required, and successful exploitation runs code in the SharePoint service account context.

The record

CVE
CVE-2021-42309
Published
Dec 15, 2021
Updated
Aug 4, 2024
Vendor
Microsoft
Product
Microsoft SharePoint Foundation 2013
Classifications
CWE-732, CWE-94, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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 <15.0.5407.1000

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Microsoft · Microsoft SharePoint Foundation 2013version=15.0.0 <15.0.5407.1000
Microsoft · Microsoft SharePoint Enterprise Server 2016version=16.0.0 <16.0.5254.1000
Microsoft · Microsoft SharePoint Server 2019version=16.0.0 <16.0.10381.20001
Microsoft · Microsoft SharePoint Server Subscription Editionversion=16.0.0 <16.0.14326.20620

Published CVSS scores

6.5NIST NVDAV:N/AC:L/Au:S/C:P/I:P/A:P
8.8Microsoft CorporationCVSS: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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-732Incorrect Permission Assignment for Critical Resource
CWE-94Improper Control of Generation of Code ('Code Injection')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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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