KB5002856 — Security Update for SharePoint Server 2019 Language Pack

Overview

KB5002856 is a critical security update released on April 14, 2026, for Microsoft SharePoint Server 2019 Language Pack components. This update addresses multiple high-severity vulnerabilities that could allow attackers to execute arbitrary code, escalate privileges, or access sensitive information in SharePoint environments with language pack installations.

Security Vulnerabilities Addressed

This security update resolves several critical vulnerabilities in SharePoint Server 2019 Language Pack components:

Cross-Site Scripting (XSS) Vulnerabilities

Multiple XSS vulnerabilities in language-specific web parts could allow authenticated attackers to inject malicious scripts into SharePoint pages. These vulnerabilities specifically affect multilingual text fields, custom actions, and localized display components where user input was not properly sanitized before rendering.

Remote Code Execution Flaws

Critical vulnerabilities in language pack file processing routines could allow attackers to execute arbitrary code on SharePoint servers. These flaws occur during the installation and processing of language pack files, where insufficient validation of file contents could lead to buffer overflows and code injection.

Elevation of Privilege Issues

Security flaws in multilingual content rendering components could allow users to gain unauthorized access to restricted SharePoint resources. These vulnerabilities stem from improper permission validation when accessing language-specific content and resources.

Information Disclosure Vulnerabilities

Localized error messages and system responses could expose sensitive system information including internal file paths, configuration details, and database connection strings. This information could be leveraged by attackers to plan further attacks against SharePoint infrastructure.

Affected Systems

KB5002856 applies to the following SharePoint Server 2019 configurations:

Installation Requirements

Before installing KB5002856, ensure the following prerequisites are met:

• SharePoint Server 2019 with at least one language pack installed
• Local administrator privileges on all SharePoint servers
• Minimum 500 MB available disk space on system drive
• All SharePoint services running and accessible
• Database connectivity to SharePoint configuration and content databases

Deployment Considerations

For SharePoint farms with multiple servers, install the update on all servers in the following order:

1. Database servers (if SharePoint components are installed)
2. Application servers
3. Web front-end servers
4. Central Administration server

Run the SharePoint Products Configuration Wizard after installing the update on all servers to ensure proper configuration synchronization.

Security Impact Assessment

The vulnerabilities addressed by KB5002856 pose significant security risks to SharePoint environments:

Risk Level: Critical

The remote code execution vulnerabilities carry a critical risk rating as they could allow attackers to gain complete control over SharePoint servers. Organizations with internet-facing SharePoint sites or environments with untrusted users should prioritize this update.

Attack Vectors

Potential attack scenarios include:

• Malicious file uploads disguised as language pack resources
• Crafted requests targeting multilingual content processing
• Social engineering attacks leveraging XSS vulnerabilities in language-specific components
• Privilege escalation through exploitation of multilingual rendering flaws

Post-Installation Verification

After installing KB5002856, perform the following verification steps:

Service Health Check

Verify that all SharePoint services are running correctly:

Get-SPServiceInstance | Where-Object {$_.Status -eq "Online"}

Language Pack Functionality

Test language pack functionality by:

• Switching site language settings in Site Settings
• Verifying multilingual content displays correctly
• Testing language-specific web parts and features
• Confirming search results appear in appropriate languages

Security Validation

Validate that security fixes are properly applied by reviewing SharePoint logs for any security-related errors or warnings. Monitor the following log sources:

• SharePoint ULS logs for language pack errors
• Windows Event Log for security audit events
• IIS logs for unusual request patterns

Rollback Procedures

If issues occur after installing KB5002856, the update can be removed through the following methods:

Control Panel Uninstallation

Navigate to Programs and Features in Control Panel and locate "Security Update for Microsoft SharePoint Server 2019 Language Pack (KB5002856)" in the installed updates list.

Command Line Removal

Use the following command to remove the update:

wusa /uninstall /kb:5002856 /quiet /norestart