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+---
+gem: ruby-saml
+cve: 2025-54572
+ghsa: rrqh-93c8-j966
+url: https://github.com/SAML-Toolkits/ruby-saml/security/advisories/GHSA-rrqh-93c8-j966
+title: Ruby SAML DOS vulnerability with large SAML response
+date: 2025-07-30
+description: |
+  ### Summary
+
+  A denial-of-service vulnerability exists in ruby-saml even with the
+  message_max_bytesize setting configured. The vulnerability occurs
+  because the SAML response is validated for Base64 format prior to
+  checking the message size,  leading to potential resource exhaustion.
+
+  ### Details
+
+  `ruby-saml` includes a `message_max_bytesize` setting intended to
+  prevent DOS attacks and decompression bombs. However, this protection
+  is ineffective in some cases due to the order of operations in the code:
+
+  https://github.com/SAML-Toolkits/ruby-saml/blob/fbbedc978300deb9355a8e505849666974ef2e67/lib/onelogin/ruby-saml/saml_message.rb
+
+  ```ruby
+       def decode_raw_saml(saml, settings = nil)
+          return saml unless base64_encoded?(saml)
+  # <--- Issue here. Should be moved after next code block.
+
+          settings =  OneLogin::RubySaml::Settings.new if settings.nil?
+          if saml.bytesize > settings.message_max_bytesize
+             raise ValidationError.new(\"Encoded SAML Message exceeds \" +
+             settings.message_max_bytesize.to_s +
+             \" bytes, so was rejected\")
+          end
+          decoded = decode(saml)
+        ...
+        end
+  ```
+
+  The vulnerability is in the execution order. Prior to checking
+  bytesize the `base64_encoded?` function performs regex matching
+  on the entire input string:
+
+  ```ruby
+  !!string.gsub(/[\\r\]|\\\\r|\\\|\\s/, \"\").match(BASE64_FORMAT)
+  ```
+
+  ### Impact
+
+  _What kind of vulnerability is it? Who is impacted?_
+
+  When successfully  exploited, this vulnerability can lead to:
+  - Excessive memory consumption
+  - High CPU utilization
+  - Application slowdown or unresponsiveness
+  - Complete application crash in severe cases
+  - Potential denial of service for legitimate users
+
+  All applications using `ruby-saml` with SAML configured and
+  enabled are vulnerable.
+
+  ###   Potential Solution
+
+  Reorder the validation steps to ensure max bytesize is checked first
+
+  ```ruby
+  def decode_raw_saml(saml, settings = nil)
+    settings = OneLogin::RubySaml::Settings.new
+  if settings.nil?
+    if saml.bytesize > settings.message_max_bytesize
+      raise  ValidationError.new(\"Encoded SAML Message exceeds \" +
+      settings.message_max_bytesize.to_s  + \" bytes, so was rejected\")
+    end
+    return saml unless base64_encoded?(saml)
+    decoded = decode(saml)
+    ...
+  end
+  ```
+cvss_v4: 6.9
+patched_versions:
+  - ">= 1.18.1"
+related:
+  url:
+    - https://nvd.nist.gov/vuln/detail/CVE-2025-54572
+    - https://github.com/SAML-Toolkits/ruby-saml/security/advisories/GHSA-rrqh-93c8-j966
+    - https://github.com/SAML-Toolkits/ruby-saml/releases/tag/v1.18.1
+    - https://github.com/SAML-Toolkits/ruby-saml/pull/770
+    - https://github.com/SAML-Toolkits/ruby-saml/commit/38ef5dd1ce17514e202431f569c4f5633e6c2709
+    - https://github.com/advisories/GHSA-rrqh-93c8-j966