---
title: "CVE-2025-66567: Ruby-saml has a SAML authentication bypass due to namespace handling (parser differential)"
url: https://erroneo.us/security/cve/CVE-2025-66567/
description: "CVE-2025-66567 (ruby-saml (RubyGems)): The ruby-saml library is for implementing the client side of a SAML authorization. ruby-saml versions up to and…"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-12-09
date_modified: 2025-12-12
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-66567"
kev: false
cvss: 9.3
epss: 0.00392
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.4% , percentile 32: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 32% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes ruby-saml (RubyGems) < 1.18.0, fixed in 1.18.0 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- RubyGems `ruby-saml` < 1.18.0 → fixed: 1.18.0

## Affected products (CVE record)

- SAML-Toolkits ruby-saml: < 1.18.0

## Severity

- GitHub_M CVSS 4.0: 9.3 `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`
- GitHub CVSS 4.0: 9.3 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.39% probability of exploitation activity in the next 30 days; percentile 32.

## Sources

- [GitHub Advisory GHSA-9v8j-x534-2fx3](https://github.com/advisories/GHSA-9v8j-x534-2fx3)
- [CVE.org record CVE-2025-66567](https://www.cve.org/CVERecord?id=CVE-2025-66567)
- [NVD entry CVE-2025-66567](https://nvd.nist.gov/vuln/detail/CVE-2025-66567)
- [github.com](https://github.com/SAML-Toolkits/ruby-saml/security/advisories/GHSA-9v8j-x534-2fx3)
- [github.com](https://github.com/SAML-Toolkits/ruby-saml/commit/e9c1cdbd0f9afa467b585de279db0cbd0fb8ae97)
- [github.com](https://github.com/advisories/GHSA-754f-8gm6-c4r2)
- [github.com](https://github.com/rubysec/ruby-advisory-db/blob/master/gems/ruby-saml/CVE-2025-66567.yml)

---
Source page: https://erroneo.us/security/cve/CVE-2025-66567/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt