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CVE-2017-11427

Manipulation of SAML data without invalidating the cryptographic signature in OneLogin PythonSAML (2.3.0 and earlier)

  • CVSS 9.8
  • CWE-287
  • Cryptographic
  • Remote

OneLogin PythonSAML 2.3.0 and earlier may incorrectly utilize the results of XML DOM traversal and canonicalization APIs in such a way that an attacker may be able to manipulate the SAML data without invalidating the cryptographic signature, allowing the attack to potentially bypass authentication to SAML service providers.

CVE
CVE-2017-11427
CWE
CWE-287
CVSS base score
9.8
Published
2019-04-17
OWASP
A04 Insecure Design
Orthogonal defect classification
Function
Code defect classification
Incorrect Functionality
Category
Cryptographic
Subcategory
Cryptographic Implementation Error
Accessibility scope
Remote
Impact
Unauthorized Access
Fixed by upgrading
Yes

Solution

Update to OneLogin PythonSAML version 2.3.1 or higher

Vulnerable code sample

import xml.etree.ElementTree as ET
import xmlsec

def validate_saml_response(saml_response):
    """Vulnerable function that demonstrates the security issue."""
    # VULNERABLE: This code is susceptible to path traversal
    root = ET.fromstring(saml_response)

    xml_data = ET.tostring(root, method='xml', encoding='utf-8')

    key = xmlsec.Key.from_file('path/to/public_key.pem', xmlsec.KeyFormat.PEM)
    signature_context = xmlsec.SignatureContext(key)

    signature_template = xmlsec.template.create(root, xmlsec.TransformExclC14N, xmlsec.TransformSignature)
    signature_context.verify(signature_template)

    return True

saml_response = '''<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">...</samlp:Response>'''
if validate_saml_response(saml_response):
    print("SAML response is valid and signature is verified.")
else:
    print("Invalid SAML response or signature.")

Patched code sample

import defusedxml.ElementTree as ET
import xmlsec

def validate_saml_response(saml_response):
    """Secure function that fixes the vulnerability."""
    # SECURE: This version prevents path traversal
    root = ET.fromstring(saml_response)

    signature_node = xmlsec.tree.find_node(root, xmlsec.Node.SIGNATURE)
    if signature_node is None:
        raise ValueError("No Signature node found in SAML response.")

    key = xmlsec.Key.from_file('path/to/public_key.pem', xmlsec.KeyFormat.PEM)

    ctx = xmlsec.SignatureContext()
    ctx.key = key
    ctx.verify(signature_node)

    return True

saml_response = '''<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol">...</samlp:Response>'''

try:
    if validate_saml_response(saml_response):
        print("SAML response is valid and signature is verified.")
except Exception as e:
    print(f"Validation failed: {e}")

Cite this entry

@misc{vaitp:cve201711427,
  title        = {{Manipulation of SAML data without invalidating the cryptographic signature in OneLogin PythonSAML (2.3.0 and earlier)}},
  author       = {Bogaerts, Fr\'ed\'eric and Ivaki, Naghmeh and Fonseca, Jos\'e},
  year         = {2019},
  note         = {VAITP Python Vulnerability Dataset, entry CVE-2017-11427},
  howpublished = {\url{https://netpack.pt/vaitp/vulnerability/CVE-2017-11427/}}
}
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