Authenticated XSS via unsanitized web request
Published May 21, 2020 · Updated Aug 19, 2026
Cross-site scripting in SharePoint Server 2016 and 2019 allows remote authenticated users to execute script through a crafted web request. SharePoint's request-processing path fails to sanitize attacker-controlled request data before returning it in browser-rendered content; Microsoft has not identified a more specific handler or parameter. Exploitation requires SharePoint authentication and victim interaction, and the script runs in the victim's security context to read unauthorized content, act as that user, change permissions, delete content, or inject browser content.
Summary
What happened
Cross-site scripting in SharePoint Server 2016 and 2019 allows remote authenticated users to execute script through a crafted web request. SharePoint's request-processing path fails to sanitize attacker-controlled request data before returning it in browser-rendered content; Microsoft has not identified a more specific handler or parameter. Exploitation requires SharePoint authentication and victim interaction, and the script runs in the victim's security context to read unauthorized content, act as that user, change permissions, delete content, or inject browser content.
The record
- CVE
- CVE-2020-1099
- Published
- May 21, 2020
- Updated
- Aug 19, 2026
- Vendor
- Microsoft
- Product
- Microsoft SharePoint Enterprise Server 2016
- Classifications
- CWE-79, T1059.007
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- May 21, 2020CVE publishedPublication date reported by the CVE source.
- Aug 19, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=16.0.0 <publication
What conditions does exploitation require?
What is affected?
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.
Weakness, pattern, technique
Public exploit references
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Your stack
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