Ruby-saml allows a Libxml2 Canonicalization error to bypass Digest/Signature validation

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

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 · score source

EPSS

• CVE-2025-66568: 0.25% estimated exploitation activity in the next 30 days; percentile 16.39 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Ruby-saml up to and including 1.12.4, there is an authentication bypass vulnerability because of an issue at libxml2 canonicalization process used by Nokogiri for document transformation. That allows an attacker to be able to execute a Signature Wrapping attack. The vulnerability does not affect the version 1.18.0. Details 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. Impact 1. Digest bypass: By crafting input that causes canonicalization to yield an empty string, the attacker can manipulate validation to pass incorrectly. 2. Signature replay on empty canonical form: If an empty string has been signed once (e.g., in a prior interaction or via a misconfigured flow), that signature can potentially be replayed to bypass authentication.

Published by the source

8 Dec 2025, 22:03 UTC

Last modified by the source

12 Dec 2025, 21:53 UTC

Source last checked

26 Oct 2026, 15:51 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-x4h9-gwv3-r4m4

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# Patch Next advisory brief: CVE-2025-66568

Advisory: Ruby-saml allows a Libxml2 Canonicalization error to bypass Digest/Signature validation
IDs: CVE-2025-66568, GHSA-x4h9-gwv3-r4m4
Record: https://patchnext.com/advisories/cve-2025-66568 (revision 1, source checked 26 Oct 2026, 15:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ruby-saml 1.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- RubyGems ruby-saml: affected < 1.18.0; fixed in 1.18.0

## Suggested inspection (read-only)
- RubyGems ruby-saml: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on ruby-saml.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-x4h9-gwv3-r4m4 (GitHub-reviewed advisory GHSA-x4h9-gwv3-r4m4 lists affected ranges: RubyGems ruby-saml >=0 <1.18.0)

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