CVE-2021-20839 : Exploit Details and Defense Strategies

This article provides details about CVE-2021-20839, a vulnerability found in Office Server Document Converter software.

Understanding CVE-2021-20839

This CVE ID pertains to a security issue in Antenna House, Inc.'s Office Server Document Converter software that allows a remote unauthenticated attacker to exploit an XML External Entity (XXE) vulnerability.

What is CVE-2021-20839?

The vulnerability in Office Server Document Converter V7.2MR4 and earlier, as well as V7.1MR7 and earlier, enables a remote unauthenticated attacker to launch an XML External Entity (XXE) attack. By processing a maliciously crafted XML document, the attacker can trigger a denial of service (DoS) condition on other servers.

The Impact of CVE-2021-20839

This security flaw can result in a denial of service (DoS) condition, potentially disrupting the availability and functionality of servers running the vulnerable versions of Office Server Document Converter.

Technical Details of CVE-2021-20839

The following technical aspects are associated with CVE-2021-20839:

Vulnerability Description

The vulnerability allows a remote unauthenticated attacker to exploit an XML External Entity (XXE) flaw, leading to a denial of service (DoS) risk on other servers.

Affected Systems and Versions

Office Server Document Converter versions V7.2MR4 and earlier, and V7.1MR7 and earlier, are affected by this vulnerability.

Exploitation Mechanism

Attackers can exploit this vulnerability by sending a specially crafted XML document to the affected server, triggering the XXE attack and causing a DoS condition.

Mitigation and Prevention

To address CVE-2021-20839, users and organizations are advised to take the following steps:

Immediate Steps to Take

Update Office Server Document Converter to the latest patched version.
Implement network security controls to restrict unauthorized access.

Long-Term Security Practices

Regularly update software and apply security patches promptly.
Conduct security assessments and audits to identify vulnerabilities.

Patching and Updates

Vendor-provided patches should be applied as soon as they are released to mitigate the risk associated with CVE-2021-20839.