xml-crypto, Signature Verification Bypass, CVE-2023-XXXX (Critical)

How the CVE Works:

This vulnerability in xml-crypto (versions <= 6.0.0) allows attackers to bypass signature verification in signed XML documents. The issue arises due to improper handling of comments within the `` element. Attackers can inject comments into the `` field, which are ignored during signature validation. This enables tampering with the XML content while still passing verification checks. For example, an attacker could modify SAML assertions to escalate privileges or impersonate users. The vulnerability is critical as it impacts systems relying on XML-based authentication and authorization mechanisms, such as SAML, where tampered XML documents can lead to unauthorized access.

DailyCVE Form:

Platform: xml-crypto
Version: <= 6.0.0
Vulnerability: Signature Bypass
Severity: Critical
Date: 2023-XX-XX

What Undercode Say:

Exploitation:

1. Tampering with XML: Attackers inject comments into the `` element of signed XML documents.

Example:

<DigestValue>
<!--TBlYWE0ZWM4ODI1NjliYzE3NmViN2E1OTlkOGDhhNmI=-->
c7RuVDYo83z2su5uk0Nla8DXcXvKYKgf7tZklJxL/LZ=
</DigestValue>

2. Bypassing Verification: The modified XML still passes signature validation, allowing unauthorized changes.

Detection:

1. Check for Comments: Use XPath to detect comments in <DigestValue>:

   const xpath = require('xpath');
   const dom = require('xmldom').DOMParser;
   const decryptedDocument = new dom().parseFromString(decryptedXML);
   const digestValues = xpath.select(
   "//[bash][bash]",
   decryptedDocument,
   );
   if (digestValues.length > 0) {
   console.log("Compromise detected!");
   }
   

2. Log Analysis: Monitor XML payloads for unusual patterns or comments in critical fields.

Mitigation:

1. Upgrade: Update xml-crypto to version 6.0.1 or later.

   npm install xml-crypto@latest
   

2. Input Validation: Reject XML documents containing comments in <DigestValue>.
3. Signature Revalidation: Implement additional checks to ensure the integrity of signed XML documents.

References:

• bash
• bash

Commands:

• Check Installed Version:

  npm list xml-crypto
  

• Upgrade Package:

  npm install [email protected]
  

• Test for Vulnerability:

  const xpath = require('xpath');
  const dom = require('xmldom').DOMParser;
  const fs = require('fs');
  const xml = fs.readFileSync('saml_response.xml', 'utf8');
  const doc = new dom().parseFromString(xml);
  const digestValues = xpath.select(
  "//[bash][bash]",
  doc,
  );
  if (digestValues.length > 0) {
  console.log("Vulnerable XML detected!");
  }
  

  By following these steps, you can exploit, detect, and protect against this critical vulnerability in xml-crypto.

References:

Reported By: https://github.com/advisories/GHSA-x3m8-899r-f7c3
Extra Source Hub:
Undercode

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