CVE-2021-21294 : Exploit Details and Defense Strategies

Http4s (http4s-blaze-server) before versions 0.21.17, 0.22.0-M2, and 1.0.0-M14 contains a vulnerability that can lead to denial-of-service attacks. The issue arises from unbounded connection acceptance in Blaze-core, affecting http4s-blaze-server users.

Understanding CVE-2021-21294

This article delves into the impact and technical details of CVE-2021-21294.

What is CVE-2021-21294?

Http4s (http4s-blaze-server) vulnerability allows unbounded connections, leading to denial-of-service attacks by draining the OS resources through Blaze-core.

The Impact of CVE-2021-21294

With a CVSS base score of 7.5 (High), the vulnerability can severely impact service availability, amplifying degradation for overloaded services.

Technical Details of CVE-2021-21294

Let's explore the vulnerability specifics and affected systems.

Vulnerability Description

The flaw lies in unbounded connection acceptance in Blaze-core, allowing unlimited connections and draining OS resources, affecting service availability.

Affected Systems and Versions

Http4s versions prior to 0.21.17, 0.22.0-M2, and 1.0.0-M14 are impacted by this vulnerability.

Exploitation Mechanism

By unboundedly accepting connections, the vulnerability escalates service degradation, impacting service reliability.

Mitigation and Prevention

Here are the steps to mitigate the impact and prevent future exploitation.

Immediate Steps to Take

Update http4s to version 0.21.17 or above, apply workarounds mentioned in the GitHub Advisory GHSA-xhv5-w9c5-2r2w for effective mitigation.

Long-Term Security Practices

Regularly update http4s, monitor incoming connections, and enforce connection limits to prevent resource exhaustion.

Patching and Updates

Deploy patches provided in versions 0.21.17, 0.22.0-M2, and 1.0.0-M14 to limit connections and ensure service availability.