CVE-2021-28484 : Exploit Details and Defense Strategies

Yubico yubihsm-connector before 3.0.1 (in YubiHSM SDK before 2021.04) is affected by a critical issue in the /api/connector endpoint handler. This vulnerability allows an attacker to send a specific length of bytes to cause the yubihsm-connector to hang in a loop, halting further operations until the service is restarted.

Understanding CVE-2021-28484

This section dives into the details of the vulnerability, its impact, technical aspects, and steps to mitigate the risk.

What is CVE-2021-28484?

CVE-2021-28484 is a critical vulnerability in Yubico yubihsm-connector before version 3.0.1, affecting the interaction with the /api/connector endpoint handler. The flaw allows attackers to trigger a state where the service gets stuck waiting for data, leading to a denial of service condition.

The Impact of CVE-2021-28484

The impact of this CVE is significant as it enables malicious actors to disrupt the normal functioning of the yubihsm-connector service by sending a small number of bytes. This results in a denial of service, requiring manual intervention to restore service.

Technical Details of CVE-2021-28484

In this section, we explore the technical aspects of the vulnerability, including how it can be exploited and the systems affected.

Vulnerability Description

The vulnerability stems from a lack of input validation in the /api/connector endpoint handler, allowing an attacker to input a small number of bytes that trigger a loop, halting the service until it is restarted.

Affected Systems and Versions

Yubico yubihsm-connector versions before 3.0.1 (YubiHSM SDK before 2021.04) are impacted by this vulnerability. Users of these versions are at risk of a denial of service due to the mentioned issue.

Exploitation Mechanism

To exploit this vulnerability, an attacker can send 0, 1, or 2 bytes to the /api/connector endpoint. This triggers the yubihsm-connector to get stuck in a loop, rendering it unresponsive until manual intervention.

Mitigation and Prevention

This section outlines the steps to mitigate the risks associated with CVE-2021-28484 and prevent exploitation.

Immediate Steps to Take

Users are advised to update to version 3.0.1 of Yubico yubihsm-connector or YubiHSM SDK version 2021.04 to patch the vulnerability and prevent attackers from triggering the denial of service condition.

Long-Term Security Practices

In addition to applying the patch, it is recommended to follow secure coding practices, implement input validation, and regularly update software to prevent such vulnerabilities from being exploited.

Patching and Updates

Regularly check for updates from Yubico and apply patches promptly to ensure your systems are protected against known vulnerabilities.