CVE-2026-34835 (Medium) detected in rack-3.1.16.gem

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
72/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
ruby
Domain
backend, security

Research direction

Start with /Gemfile.lock and /vendor/cache/rack-3.1.16.gem, then inspect the dependency chain through rubocop-rails. Update Rack to a patched release, 3.1.21 or 3.2.6, and verify the lockfile and vendored artifact no longer contain 3.1.16.

Written by the indexing model from the issue text.

Description

Mend: dependency security vulnerability

CVE-2026-34835 - 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
      • ❌ rack-3.1.16.gem (Vulnerable Library)

Found in base branch: master

Vulnerability Details

Rack is a modular Ruby web server interface. From versions 3.0.0.beta1 to before 3.1.21, and 3.2.0 to before 3.2.6, Rack::Request parses the Host header using an AUTHORITY regular expression that accepts characters not permitted in RFC-compliant hostnames, including /, ?, #, and @. Because req.host returns the full parsed value, applications that validate hosts using naive prefix or suffix checks can be bypassed. This can lead to host header poisoning in applications that use req.host, req.url, or req.base_url for link generation, redirects, or origin validation. This issue has been patched in versions 3.1.21 and 3.2.6.

Publish Date: 2026-04-02

URL: CVE-2026-34835

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-g2pf-xv49-m2h5

Release Date: 2026-04-02

Fix Resolution: rack - 3.2.6,rack - 3.1.21

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Dominant language
Ruby
Stars
30
Forks
27
No merged PRs in 30d

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