CVE-2025-27610: Rack Path Traversal Vulnerability

CVE-2025-27610 Overview

CVE-2025-27610 is a Path Traversal vulnerability in Rack, the widely-used Ruby web server interface that serves as the foundation for Ruby web frameworks including Rails and Sinatra. The vulnerability exists in the Rack::Static middleware, which incorrectly serves files under the specified root: directory even when urls: parameters are provided, potentially exposing sensitive files to unauthorized access.

The flaw arises from improper sanitization of user-supplied paths before serving files. Specifically, encoded path traversal sequences are not correctly validated, allowing attackers to access files outside the designated static file directory. An attacker who can determine file paths on the server can potentially access all files under the configured root: directory.

Critical Impact

Attackers can exploit this path traversal vulnerability to read sensitive files including configuration files, source code, and potentially credentials from Ruby web applications using the Rack::Static middleware.

Affected Products

• Rack versions prior to 2.2.13
• Rack versions 3.0.x prior to 3.0.14
• Rack versions 3.1.x prior to 3.1.12

Discovery Timeline

• 2025-03-10 - CVE-2025-27610 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2025-27610

Vulnerability Analysis

This vulnerability is classified as CWE-23 (Relative Path Traversal). The core issue lies in how Rack::Static processes URL paths when determining which files to serve. When an application configures Rack::Static with both root: and urls: parameters, the expectation is that only files matching the specified URL patterns should be accessible. However, due to insufficient path sanitization, attackers can craft requests with encoded traversal sequences that bypass these restrictions.

The vulnerability enables unauthorized file disclosure across the entire root: directory structure. Since Rack serves as the foundational middleware for most Ruby web applications, this vulnerability has a broad potential impact across the Ruby ecosystem. The network-accessible nature of this flaw means it can be exploited remotely without authentication, making it particularly concerning for publicly-facing Ruby applications.

Root Cause

The root cause is improper input validation in the Rack::Static middleware's file path handling logic. When processing incoming requests, the middleware fails to properly decode and validate path components before mapping them to the filesystem. This allows URL-encoded path traversal sequences (such as %2e%2e%2f representing ../) to slip past security checks that would normally prevent directory traversal attacks.

The middleware assumes that the urls: configuration parameter restricts file access, but the path traversal vulnerability allows attackers to escape these boundaries and access arbitrary files within the root: directory.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by sending specially crafted HTTP requests to a vulnerable Ruby web application that uses Rack::Static middleware.

The exploitation flow typically involves:

1. Identifying a target application using Rack with Rack::Static middleware
2. Crafting HTTP requests with encoded path traversal sequences
3. Accessing files outside the intended static file directory
4. Extracting sensitive information such as configuration files, database credentials, or application source code

Since no verified proof-of-concept code is available, organizations should refer to the GitHub Security Advisory for technical details on the exploitation mechanism.

Detection Methods for CVE-2025-27610

Indicators of Compromise

• HTTP access logs containing URL-encoded path traversal sequences such as %2e%2e%2f or %2e%2e/
• Unusual access patterns to files outside designated static directories
• Requests attempting to access sensitive files like config/database.yml, .env, or Gemfile
• Web server logs showing successful retrieval of files that should not be publicly accessible

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block path traversal patterns in URLs
• Monitor HTTP access logs for encoded directory traversal sequences and suspicious file access attempts
• Deploy intrusion detection systems with signatures for common path traversal attack patterns
• Use application security monitoring tools to track file access requests against expected static file patterns

Monitoring Recommendations

• Enable detailed access logging for all Ruby web applications using Rack middleware
• Set up alerts for requests containing path traversal indicators targeting static file endpoints
• Regularly audit file access logs to identify potential exploitation attempts
• Monitor for unusual spikes in 200 OK responses for file requests outside normal static asset directories

How to Mitigate CVE-2025-27610

Immediate Actions Required

• Upgrade Rack to patched versions: 2.2.13, 3.0.14, or 3.1.12 depending on your version branch
• Review application configurations to identify usage of Rack::Static middleware
• Audit the root: directory configuration to ensure it only contains files intended for public access
• Implement network-level protections such as WAF rules to block path traversal attempts while planning upgrades

Patch Information

Security patches have been released by the Rack maintainers. The fix is available in the following versions:

• Rack 2.2.13 for the 2.2.x branch
• Rack 3.0.14 for the 3.0.x branch
• Rack 3.1.12 for the 3.1.x branch

The patch can be reviewed in the GitHub commit. Additional information is available in the GitHub Security Advisory and the Debian LTS Announcement.

Workarounds

• Remove usage of Rack::Static middleware entirely if static file serving is not required
• Ensure the root: parameter points to a directory containing only files intended for public access
• Deploy a CDN or dedicated static file server (such as Nginx or Apache) in front of the application to handle static assets
• Implement strict input validation at the web server or reverse proxy level to reject requests containing path traversal patterns

# Example: Update Rack gem to patched version
bundle update rack

# Verify installed version
bundle show rack

# Alternative: Specify minimum version in Gemfile
# gem 'rack', '>= 3.1.12'