Quick answers
- Is CVE-2026-33170 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-33170 being exploited in the wild.
- How severe is CVE-2026-33170?
- Medium severity, with a CVSS score of 4, published 23 March 2026.
- Which products and versions are affected?
- activesupport (RubyGems) ECOSYSTEM:introduced=8.1.0.beta1,fixed=8.1.2.1.
- Is there a fix for CVE-2026-33170?
- Yes. activesupport (RubyGems): upgrade to 8.1.2.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-33170 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-33170?
- Check whether you run Ruby on Rails Active Support or activesupport (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- activesupport (RubyGems): upgrade to 8.1.2.1 or later
bundle update activesupport
Technical details
A vulnerability exists in Active Support's SafeBuffer#% method where it fails to correctly propagate the @html_unsafe flag to newly created buffers. If a SafeBuffer is mutated in place (using methods like gsub!) and subsequently formatted using the % operator with untrusted arguments, the resulting object incorrectly identifies as html_safe. This flaw allows an attacker to bypass ERB auto-escaping mechanisms, leading to reflected or stored XSS. The issue is resolved in versions 8.1.2.1, 8.0.4.1, and 7.2.3.1.
Affected products
- Ruby on Rails activesupport >= 8.1.0.beta1, < 8.1.2.1
- Ruby on Rails activesupport >= 8.0.0.beta1, < 8.0.4.1
- Ruby on Rails activesupport < 7.2.3.1
Identifiers
- CVE-2026-33170
- GHSA-89vf-4333-qx8v
Timeline
- 2026-03-23: disclosed
- 2026-03-23: advisory
- 2026-03-23: patched