CVE-2026-33170: Rubyonrails Rails

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

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.

Affected products

• Rubyonrails Rails: before 7.2.3.1 (fixed in 7.2.3.1); from 8.0.0, before 8.0.4.1 (fixed in 8.0.4.1); from 8.1.0, before 8.1.2.1 (fixed in 8.1.2.1)

Published 2026-03-24. Last modified 2026-06-17.