CVE-2021-21409 : Exploit Details and Defense Strategies

Netty before version 4.1.61.Final has a vulnerability that enables request smuggling due to missing validation of the content-length header. This could lead to request smuggling if proxied to a remote peer and translated to HTTP/1.1. Followup of a previous advisory that didn't fix this case.

Understanding CVE-2021-21409

This CVE affects the Netty framework, potentially enabling request smuggling in HTTP/2.

What is CVE-2021-21409?

Netty's version before 4.1.61.Final is susceptible to request smuggling due to incorrect validation of the content-length header.

The Impact of CVE-2021-21409

The impact includes a possibility of request smuggling when the request is proxied to a remote peer and translated to HTTP/1.1.

Technical Details of CVE-2021-21409

The vulnerability allows attackers to perform request smuggling if certain conditions are met.

Vulnerability Description

Netty version before 4.1.61.Final incorrectly validates the content-length header, enabling request smuggling.

Affected Systems and Versions

Systems using Netty versions earlier than 4.1.61.Final are affected by this vulnerability.

Exploitation Mechanism

Exploitation involves using a single Http2HeaderFrame with the endStream set to true to bypass content-length validation.

Mitigation and Prevention

To mitigate this issue, users are advised to update Netty to version 4.1.61.Final or higher.

Immediate Steps to Take

Upgrade Netty framework to version 4.1.61.Final or above to prevent the vulnerability exploitation.

Long-Term Security Practices

Regularly update software components to their latest versions to avoid known vulnerabilities.

Patching and Updates

Stay informed about security advisories and apply patches promptly to maintain a secure environment.