Executive Summary

This vulnerability is an HTTP Request Smuggling issue in the http4s Scala HTTP service interface. It occurs due to improper handling of the HTTP trailer section in versions from 1.0.0-M1 to before 1.0.0-M45 and before 0.23.31. Attackers can exploit this by sending specially crafted HTTP requests that bypass front-end server security controls, potentially allowing them to launch targeted attacks against active users and poison web caches. Exploitation requires the web application to be behind a reverse-proxy that forwards trailer headers. The issue has been fixed in versions 1.0.0-M45 and 0.23.31.

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Impact Analysis

This vulnerability can impact you by allowing attackers to bypass security controls on front-end servers, which may lead to unauthorized access or manipulation of web traffic. Attackers could launch targeted attacks against active users, potentially compromising user data or sessions. Additionally, they could poison web caches, causing incorrect or malicious content to be served to users.

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Mitigation Strategies

To mitigate this vulnerability, upgrade http4s to version 1.0.0-M45 or later, or 0.23.31 or later, where the issue has been patched. Additionally, ensure that your web application is not deployed behind a reverse-proxy that forwards trailer headers, as this is a pre-requisite for exploitation.

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