CVE-2026-33170 (Medium) detected in activesupport-8.1.2.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
rails, ruby
Domain
security

Research direction

Start with /Gemfile.lock and /vendor/cache/activesupport-8.1.2.gem, then inspect the dependency path through more_core_extensions. Update Active Support to a listed fixed version, such as 8.0.4.1 or 8.1.2.1, and confirm the lockfile and cached dependency no longer contain the vulnerable 8.1.2 release.

Written by the indexing model from the issue text.

Description

Mend: dependency security vulnerability

CVE-2026-33170 - Medium Severity Vulnerability

Vulnerable Library - activesupport-8.1.2.gem

A toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Rich support for multibyte strings, internationalization, time zones, and testing.

Library home page: https://rubygems.org/gems/activesupport-8.1.2.gem

Path to dependency file: /Gemfile.lock

Path to vulnerable library: /vendor/cache/activesupport-8.1.2.gem

Dependency Hierarchy:

  • manageiq-style-1.6.0.gem (Root Library)
    • more_core_extensions-4.5.1.gem
      • ❌ activesupport-8.1.2.gem (Vulnerable Library)

Found in base branch: master

Vulnerability Details

Active Support is a toolkit of support libraries and Ruby core extensions extracted from the Rails framework. Prior to versions 8.1.2.1, 8.0.4.1, and 7.2.3.1, "SafeBuffer#%" does not propagate the "@html_unsafe" flag to the newly created buffer. If a "SafeBuffer" is mutated in place (e.g. via "gsub!") and then formatted with "%" using untrusted arguments, the result incorrectly reports "html_safe? == true", bypassing ERB auto-escaping and possibly leading to XSS. Versions 8.1.2.1, 8.0.4.1, and 7.2.3.1 contain a patch.

Publish Date: 2026-03-23

URL: CVE-2026-33170

CVSS 3 Score Details (4.3)

Base Score Metrics:

  • Exploitability Metrics:
    • Attack Vector: Network
    • Attack Complexity: Low
    • Privileges Required: None
    • User Interaction: Required
    • Scope: Unchanged
  • Impact Metrics:
    • Confidentiality Impact: None
    • Integrity Impact: Low
    • Availability Impact: None

For more information on CVSS3 Scores, click here.

Suggested Fix

Type: Upgrade version

Release Date: 2026-03-23

Fix Resolution: https://github.com/rails/rails.git - v8.0.4.1,https://github.com/rails/rails.git - v7.2.3.1,https://github.com/rails/rails.git - v8.1.2.1,https://github.com/rails/rails.git - v8.1.3,https://github.com/rails/rails.git - v8.0.5

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Dominant language
Ruby
Stars
259
Forks
35
No merged PRs in 30d

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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