Observed Signal · Mar 23, 2026 · Vulnerability Disclosure · Source: DEV Community · Impact: 2/5 · Sentiment: Negative
XSS in Rails Action Pack Debug Exceptions (CVE-2026-33167)
CVE-2026-33167 is a reflected Cross-Site Scripting (XSS) vulnerability in Ruby on Rails' Action Pack debug exceptions page affecting Rails 8.1.0 through 8.1.2 (fixed in 8.1.2.1). The debug exceptions template failed to escape exception messages, allowing crafted input to inject arbitrary HTML/JavaScript into the detailed error page. The issue has a CVSS v4.0 score of 1.3, requires no authentication, and an official proof-of-concept exists in the Rails test suite. Recommended mitigations include upgrading to rails >= 8.1.2.1, disabling detailed exception pages in production (config.consider_all_requests_local = false), and applying WAF rules to block HTML tag injection. The fix removed use of the raw helper in the template; related references include a GitHub advisory (GHSA-pgm4-439c-5jp6) and commit 6752711c8c31d79ba50d13af6a6698a3b85415e0.
A low-severity XSS in a widely used web framework can affect developer and some runtime configurations; fix is available but sites using detailed debug pages or unpatched dependencies could be exposed.
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Key Takeaways & Evidence Grounding
- CVE-2026-33167 is a reflected Cross-Site Scripting (XSS) vulnerability in Ruby on Rails Action Pack debug exceptions.
- Affected versions: rails >= 8.1.0 and < 8.1.2.1; fixed in Rails v8.1.2.1.
- CVSS v4.0 score: 1.3; Attack Vector: Network; Authentication: None; Exploit status: Proof of Concept.
- Fix implemented by removing the raw helper in the debug exceptions template (commit 6752711c8c31d79ba50d13af6a6698a3b85415e0) and GitHub advisory GHSA-pgm4-439c-5jp6 published.
- Mitigations: upgrade to >= 8.1.2.1, disable detailed exception pages in production, and consider WAF rules to block HTML tag injection.
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