---
title: "CVE-2025-66568: Ruby-saml allows a Libxml2 Canonicalization error to bypass Digest/Signature validation"
url: https://erroneo.us/security/cve/CVE-2025-66568/
description: "CVE-2025-66568 (ruby-saml (RubyGems)): The ruby-saml library implements the client side of an SAML authorization. Versions up to and including 1.12.4, are…"
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-2025-66568"
kev: false
cvss: 9.3
epss: 0.00235
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2025-66568: Ruby-saml allows a Libxml2 Canonicalization error to bypass Digest/Signature validation

**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 0.2% , percentile 14: FIRST’s model estimates a 0.2% chance of exploitation activity in the next 30 days, higher than 14% 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 implements the client side of an SAML authorization. Versions up to and including 1.12.4, are vulnerable to authentication bypass through the libxml2 canonicalization process used by Nokogiri for document transformation, which allows an attacker to execute a Signature Wrapping attack. When libxml2’s canonicalization is invoked on an invalid XML input, it may return an empty string rather than a canonicalized node. ruby-saml then proceeds to compute the DigestValue over this empty string, treating it as if canonicalization succeeded. 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): 0.24% probability of exploitation activity in the next 30 days; percentile 14.

## Sources

- [GitHub Advisory GHSA-x4h9-gwv3-r4m4](https://github.com/advisories/GHSA-x4h9-gwv3-r4m4)
- [CVE.org record CVE-2025-66568](https://www.cve.org/CVERecord?id=CVE-2025-66568)
- [NVD entry CVE-2025-66568](https://nvd.nist.gov/vuln/detail/CVE-2025-66568)
- [github.com](https://github.com/SAML-Toolkits/ruby-saml/security/advisories/GHSA-x4h9-gwv3-r4m4)
- [github.com](https://github.com/SAML-Toolkits/ruby-saml/commit/acac9e9cc0b9a507882c614f25d41f8b47be349a)
- [github.com](https://github.com/rubysec/ruby-advisory-db/blob/master/gems/ruby-saml/CVE-2025-66568.yml)

---
Source page: https://erroneo.us/security/cve/CVE-2025-66568/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt