Rack is a popular and modular web server interface used in the Ruby programming world. It was designed to enable developers to build web applications more easily by providing a common point of contact between applications and web servers. However, a log injection vulnerability (CVE-2025-27111) was recently discovered in the Rack::Sendfile middleware, which might expose your applications to potential attacks if not addressed properly. This post will explain in detail what the vulnerability entails, how it can be exploited, and what you can do to secure your Ruby server and applications.
The Vulnerability
The Rack::Sendfile middleware is responsible for logging unsanitised header values coming from the X-Sendfile-Type header. Attackers can exploit this vulnerability by injecting escape sequences (such as newline characters) into this header value, which can lead to log injection. In turn, this could compromise your application by allowing attackers to manipulate your log files, causing potential issues and obfuscating genuine security warnings.
Code Snippet
An example of exploiting the vulnerability using an HTTP request and injecting newline characters into the X-Sendfile-Type header could look like this:
GET /sample_path HTTP/1.1
Host: victim.com
X-Sendfile-Type: \r\nInjected-Log-Entry: I am an attacker\r\n
The attacker could insert various commands or log entries to cause confusion and mislead administrators into wrongly diagnosing security issues and/or covering their tracks.
Mitigation
To protect your Ruby server and applications from this log injection vulnerability, it is recommended to upgrade to one of the non-vulnerable versions of Rack (2.2.12, 3..13, 3.1.11) as soon as possible.
If upgrading is not an immediate option, you can manually sanitize your log files by removing any newline characters and/or escape sequences from the X-Sendfile-Type header values before they are logged in the Rack::Sendfile middleware.
For more information on the vulnerability, please refer to the following links
- Rack GitHub Repository Issue
- Rack Middleware CVE Details
Conclusion
As a Ruby developer or administrator, it is essential to always be vigilant of potential security vulnerabilities in the tools and libraries you use. In this case, the CVE-2025-27111 vulnerability in Rack poses a log injection threat that could be exploited by attackers. To combat this issue, ensure you upgrade to the latest, secure releases of Rack and sanitize your header values when necessary, keeping your applications and servers safe from potential harm.
Timeline
Published on: 03/04/2025 16:15:40 UTC