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XML signature verification bypass due improper verification of signature / signature spoofing

Critical
cjbarth published GHSA-2xp3-57p7-qf4v May 1, 2024

Package

npm xml-crypto (npm)

Affected versions

>=4.0.0, <6.0.0

Patched versions

6.0.0

Description

Summary

Default configuration does not check authorization of the signer, it only checks the validity of the signature per section 3.2.2 of https://www.w3.org/TR/2008/REC-xmldsig-core-20080610/#sec-CoreValidation. As such, without additional validation steps, the default configuration allows a malicious actor to re-sign an XML document, place the certificate in a <KeyInfo /> element, and pass xml-crypto default validation checks.

Details

Affected xml-crypto versions between versions >= 4.0.0 and < 6.0.0.

xml-crypto trusts by default any certificate provided via digitally signed XML document's <KeyInfo />.

xml-crypto prefers to use any certificate provided via digitally signed XML document's <KeyInfo /> even if library was configured to use specific certificate (publicCert) for signature verification purposes.

Attacker can spoof signature verification by modifying XML document and replacing existing signature with signature generated with malicious private key (created by attacker) and by attaching that private key's certificate to <KeyInfo /> element.

Vulnerability is combination of changes introduced to 4.0.0 at

Changes at PR provided default method to extract certificate from signed XML document.

  • SignedXml.getCertFromKeyInfo = function (keyInfo) {
    if (keyInfo != null && keyInfo.length > 0) {
    const certs = xpath.select(".//*[local-name(.)='X509Certificate']", keyInfo[0]);
    if (certs.length > 0) {
    return utils.derToPem(certs[0].textContent.trim(), "CERTIFICATE");
    }
    }
    return null;
    };
  • this.getCertFromKeyInfo = SignedXml.getCertFromKeyInfo;

and changes at PR prefer output of that method to be used as certificate for signature verification even in the case when library is configured to use specific/pre-configured signingCert

Name of the signingCert was changed later (but prior to 4.0.0 release) to publicCert:

Issue was fixed to 6.0.0 by disabling implicit usage of default getCertFromKeyInfo implementation:

Possible workarounds for versions 4.x and 5.x:

  • Check the certificate extracted via getCertFromKeyInfo against trusted certificates before accepting the results of the validation.
  • Set xml-crypto's getCertFromKeyInfo to () => undefined forcing xml-crypto to use an explicitly configured publicCert or privateKey for signature verification.

PoC

#399

Impact

An untrusted certificate can be used to pass a malicious XML payload through an improperly configured installation of xml-crypto.

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

CVE ID

CVE-2024-32962

Weaknesses