CVE-2021-21239

PySAML2 before 6.5.0: Improper SAML signature verification

• CVSS 6.5
• CWE-347 Improper Verification of Cryptographic Signature
• Cryptographic
• Remote

PySAML2 is a pure python implementation of SAML Version 2 Standard. PySAML2 before 6.5.0 has an improper verification of cryptographic signature vulnerability. Users of pysaml2 that use the default CryptoBackendXmlSec1 backend and need to verify signed SAML documents are impacted. PySAML2 does not ensure that a signed SAML document is correctly signed. The default CryptoBackendXmlSec1 backend is using the xmlsec1 binary to verify the signature of signed SAML documents, but by default xmlsec1 accepts any type of key found within the given document. xmlsec1 needs to be configured explicitly to only use only _x509 certificates_ for the verification process of the SAML document signature. This is fixed in PySAML2 6.5.0.

CVE

CVE-2021-21239

CWE

CWE-347 Improper Verification of Cryptographic Signature

CVSS base score

6.5

Published

2021-01-21

OWASP

A08 Software and Data Integrity Failures

Orthogonal defect classification

Checking

Code defect classification

Incorrect Check

Category

Cryptographic

Subcategory

Cryptographic Implementation Error

Accessibility scope

Remote

Impact

Unauthorized Access

Fixed by upgrading

Yes

Solution

Update PySAML2 to version 6.5.0 or higher.

from saml2 import saml
from saml2.sigver import SignatureVerifier
from saml2.config import Config
from saml2.backend import InMemory

config = Config().load({
})

backend = InMemory(config)

verifier = SignatureVerifier(backend)

def verify_signed_saml_document(signed_document):
    """Vulnerable function that demonstrates the security issue."""
    try:
        saml_response = saml.from_string(signed_document)
        
        if verifier.verify(saml_response):
            print("Signature is valid.")
        else:
            print("Signature verification failed.")
    except Exception as e:
        print(f"An error occurred during verification: {e}")

signed_saml = "<Your Signed SAML Document Here>"
verify_signed_saml_document(signed_saml)

from saml2 import saml, sigver
from saml2.sigver import SignatureVerifier
from saml2.config import Config
from saml2.backend import InMemory

config = Config().load({
})

backend = InMemory(config)

verifier = SignatureVerifier(backend, use_x509=True)

def verify_signed_saml_document(signed_document):
    """Secure function that fixes the vulnerability."""
    try:
        saml_response = saml.from_string(signed_document)
        
        if verifier.verify(saml_response):
            print("Signature is valid.")
        else:
            print("Signature verification failed.")
    except Exception as e:
        print(f"An error occurred during verification: {e}")

signed_saml = "<Your Signed SAML Document Here>"
verify_signed_saml_document(signed_saml)

@misc{vaitp:cve202121239,
  title        = {{PySAML2 before 6.5.0: Improper SAML signature verification}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2021},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2021-21239},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2021-21239/}}
}