Researchers Thai Do and Minh Pham have exposed multiple critical vulnerabilities in the Rack Ruby framework, a cornerstone of Ruby-based web applications with over a billion global downloads.
Identified as CVE-2025-25184, CVE-2025-27111, and CVE-2025-27610, these flaws pose significant risks to applications built on frameworks like Ruby on Rails and Sinatra.
Rack, acting as a modular interface between web servers and Ruby applications, standardizes HTTP request and response handling, making its widespread adoption a double-edged sword when vulnerabilities emerge.
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Among the discovered issues, CVE-2025-25184 and CVE-2025-27111 enable attackers to manipulate log content through CRLF (Carriage Return Line Feed) injection and malicious header values, respectively, while CVE-2025-27610 stands out as particularly severe due to its potential for unauthorized file access via path traversal.
Deep Dive into CVE-2025-27610: Path Traversal Threat
The most alarming of these vulnerabilities, CVE-2025-27610, identified by Minh Pham, is a path traversal flaw in Rack::Static, a middleware component used to serve static files like images and CSS in Ruby applications.
Assigned a CVSS score of 7.5, marking it as a high-severity risk, this vulnerability arises from improper handling of the :root option in Rack::Static configurations.
When the :root parameter-intended to define the base directory for serving files-is not explicitly set, Rack defaults to the current working directory (Dir.pwd).
According to the Report, this oversight, coupled with a lack of adequate input validation, allows attackers to craft malicious requests using directory traversal sequences (e.g., “../”) within the PATH_INFO of an HTTP request.
By exploiting this, unauthenticated attackers can access sensitive files outside the intended directory, potentially retrieving configuration data, credentials, or other confidential information, leading to severe data breaches.
Minh Pham’s analysis of Rack’s source code revealed that the middleware directly concatenates user-supplied paths with the root directory without proper normalization or sanitization, creating a clear exploitation path.
This vulnerability’s impact is amplified by Rack’s integration into numerous Ruby ecosystems, where misconfigurations or omissions in setting the :root option are not uncommon.
A proof of concept developed on Rack version 3.1.10 demonstrated how attackers could leverage this flaw to access restricted files, underscoring the urgency of addressing this issue.
Meanwhile, CVE-2025-25184 and CVE-2025-27111, discovered by Thai Do and Minh Pham respectively, pose additional threats by allowing log injection and manipulation-an often-overlooked attack vector that can obscure malicious activities or mislead administrators during forensic investigations.
The combined effect of these vulnerabilities highlights a pressing need for developers to scrutinize their Rack configurations and apply mitigation measures.
Patching these flaws, explicitly defining secure root directories, and implementing strict input validation are critical steps to safeguard applications.
As the Ruby community braces for potential exploits, this discovery serves as a stark reminder of the importance of rigorous security practices in widely adopted frameworks like Rack, where a single oversight can ripple across countless systems worldwide.
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