CVE-2021-21348 : Security Advisory and Response

XStream, a Java library for object serialization to XML, is vulnerable to a Regular Expression Denial of Service (ReDoS) attack before version 1.4.16. This vulnerability could be exploited by a remote attacker to cause a denial of service condition by occupying CPU resources. Users are advised to update to at least version 1.4.16 for mitigation.

Understanding CVE-2021-21348

This section provides insights into the vulnerability, its impact, affected systems, and mitigation strategies.

What is CVE-2021-21348?

CVE-2021-21348 involves a vulnerability in XStream that may enable a malicious actor to exploit Regular Expression for a Denial of Service (ReDoS) attack. By consuming high CPU resources, the attacker can disrupt services and impact availability

The Impact of CVE-2021-21348

The vulnerability's impact is rated as medium severity with a CVSS base score of 5.3. This can result in high availability impact, requiring user interaction for exploitation, making it a critical security concern.

Technical Details of CVE-2021-21348

This section outlines the specifics of the vulnerability, including the description, affected systems and versions, and exploitation mechanism.

Vulnerability Description

XStream's vulnerability prior to version 1.4.16 allows a remote attacker to consume maximum CPU time, leading to a denial of service condition due to improper Regular Expression handling.

Affected Systems and Versions

The affected product is XStream by x-stream, versions below 1.4.16. Users relying on XStream's default blacklist of the Security Framework are at risk and should upgrade to the recommended version.

Exploitation Mechanism

The vulnerability can be exploited remotely, requiring no privileges to impact the availability of the system. Attackers can exhaust CPU resources through specially crafted Regular Expressions.

Mitigation and Prevention

This section provides guidance on immediate steps to take, long-term security practices, and the importance of timely patching and updates.

Immediate Steps to Take

Users are strongly advised to update XStream to version 1.4.16 or higher to mitigate the vulnerability. Additionally, implementing a security framework with minimal required types can reduce the risk of exploitation.

Long-Term Security Practices

Developers should practice secure coding techniques, validate user input, and regularly review and update dependencies to prevent similar vulnerabilities in the future.

Patching and Updates

Regularly monitor for security updates and apply patches promptly. Stay informed about security advisories from XStream and related vendors to protect systems from known vulnerabilities.