CVE-2026-34831 (Medium) detected in rack-3.1.16.gem

Nobody has claimed this yet.

## CVE-2026-34831 - Medium Severity Vulnerability
Vulnerable Library - rack-3.1.16.gem

Rack provides a minimal, modular and adaptable interface for developing
web applications in Ruby. By wrapping HTTP requests and responses in
the simplest way possible, it unifies and distills the API for web
servers, web frameworks, and software in between (the so-called
middleware) into a single method call.

Library home page: https://rubygems.org/gems/rack-3.1.16.gem

Path to dependency file: /Gemfile.lock

Path to vulnerable library: /vendor/cache/rack-3.1.16.gem

Dependency Hierarchy:
- manageiq-style-1.3.3.gem (Root Library)
- rubocop-rails-2.32.0.gem
- :x: **rack-3.1.16.gem** (Vulnerable Library)

Found in base branch: master

Vulnerability Details

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

Publish Date: 2026-04-02

URL: CVE-2026-34831

CVSS 3 Score Details (4.8)

Base Score Metrics:
- Exploitability Metrics:
- Attack Vector: Network
- Attack Complexity: High
- Privileges Required: None
- User Interaction: None
- Scope: Unchanged
- Impact Metrics:
- Confidentiality Impact: Low
- Integrity Impact: Low
- Availability Impact: None

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Origin: https://github.com/advisories/GHSA-q2ww-5357-x388

Release Date: 2026-04-02

Fix Resolution: rack - 3.1.21,rack - 3.2.6,rack - 2.2.23

***
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Start with /Gemfile.lock and the vendored dependency at /vendor/cache/rack-3.1.16.gem, then inspect the dependency hierarchy showing rack is pulled through rubocop-rails. Update the resolved Rack version to one of the listed fixed releases and verify that the lockfile and vendored package no longer contain 3.1.16.

Written by the indexing model from the issue text.