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CVE-2026-33170 — Vulnerability in activesupport — CVE Details

MEDIUM

Rails Active Support has a possible XSS vulnerability in SafeBuffer#%

Published March 23, 2026Updated September 10, 2026Source: osv

Summary

### Impact `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. ### Releases The fixed releases are available at the normal locations. ### Credit This issue was responsibly reported by @ch4n3-yoon

Advisory Timeline

  • First published March 23, 2026 (203 days ago).
  • Last revised September 10, 2026 — 170 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Bundler
Update activesupport to 7.2.3.1 or later
gem install activesupport -v 7.2.3.1
Bundler
Update activesupport to 8.1.2.1 or later
gem install activesupport -v 8.1.2.1
Bundler
Update activesupport to 8.0.4.1 or later
gem install activesupport -v 8.0.4.1

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (3)

Affects 1 ecosystem: rubygems (1).

PackageEcosystemAffectedFixed In
activesupport
rubygems
1.0.0, 1.0.1, 1.0.2, 1.0.3 (+478 more)7.2.3.1
activesupport
rubygems
8.1.0, 8.1.0.beta1, 8.1.0.rc1, 8.1.1 (+1 more)8.1.2.1
activesupport
rubygems
8.0.0, 8.0.0.1, 8.0.0.beta1, 8.0.0.rc1 (+6 more)8.0.4.1

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

  • CWE-79
    Cross-site Scripting (XSS)MITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 4.3 score means for each attack dimension.

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
P
Scope
—
Confidentiality
—
Integrity
—
Availability
—

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

References

Frequently Asked Questions

What is CVE-2026-33170?
Rails Active Support has a possible XSS vulnerability in SafeBuffer#% This vulnerability has been assigned a severity rating of MEDIUM (CVSS score: 4.3/10).
How do I check if my project is affected by CVE-2026-33170?
CVE-2026-33170 affects activesupport. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-33170 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score
4.3

Exploitation requires specific conditions or has limited impact. Remediate within weeks.

Also Known As

GHSA-89vf-4333-qx8v

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