CVE-2021-25833 : Security Advisory and Response

A file extension handling issue in ONLYOFFICE DocumentServer versions 4.2.0.71 to 5.6.0.21 allows attackers to control file extensions through request data, leading to arbitrary file overwriting and potential remote code execution.

Understanding CVE-2021-25833

This CVE identifies a critical vulnerability in ONLYOFFICE DocumentServer that can be exploited by remote attackers to compromise the application.

What is CVE-2021-25833?

CVE-2021-25833 highlights a file extension handling flaw in the [server] module of ONLYOFFICE DocumentServer v4.2.0.71 to v5.6.0.21. Attackers can manipulate file extensions via request data, enabling them to overwrite files and execute malicious code remotely.

The Impact of CVE-2021-25833

The impact of this vulnerability is severe as it allows remote attackers to achieve arbitrary file overwriting and potentially gain remote code execution capabilities on the vulnerable DocumentServer.

Technical Details of CVE-2021-25833

This section delves into specific technical aspects of the CVE to provide a deeper understanding of the issue.

Vulnerability Description

The vulnerability arises from a file extension handling flaw in the [server] module of ONLYOFFICE DocumentServer v4.2.0.71-v5.6.0.21. Attackers can exploit this to manipulate file extensions via request data, leading to arbitrary file overwriting and remote code execution.

Affected Systems and Versions

ONLYOFFICE DocumentServer versions 4.2.0.71 to 5.6.0.21 are specifically impacted by this vulnerability, making systems running these versions susceptible to exploitation.

Exploitation Mechanism

Remote attackers can trigger the vulnerability by controlling file extensions through malicious request data, granting them the ability to overwrite files and execute arbitrary code remotely.

Mitigation and Prevention

To safeguard systems against CVE-2021-25833, immediate and long-term security measures need to be implemented.

Immediate Steps to Take

Update ONLYOFFICE DocumentServer to a patched version that addresses the file extension handling issue.
Monitor network traffic for any suspicious activity that could indicate exploitation attempts.

Long-Term Security Practices

Regularly review and update security configurations to prevent similar vulnerabilities in the future.
Conduct security audits and penetration testing to identify and address potential weaknesses proactively.

Patching and Updates

Stay informed about security patches and updates released by ONLYOFFICE for DocumentServer. Promptly apply all relevant patches to ensure protection against known vulnerabilities.