CVE-2021-21238: SAML XML Signature wrapping
Impact
All users of pysaml2 that use the default CryptoBackendXmlSec1 backend and need to verify signed SAML documents are impacted. pysaml2 <= 6.4.1 does not validate the SAML document against an XML schema. This allows invalid XML documents to trick the verification process, by presenting elements with a valid signature inside elements whose content has been malformed. The verification is offloaded to xmlsec1 and xmlsec1 will not validate every signature in the given document, but only the first it finds in the given scope.
Patches
Users should upgrade to pysaml2 v6.5.0.
Workarounds
No workaround provided at this point.
References
No references provided at this point.
Credits
- Victor Schönfelder Garcia (isits AG International School of IT Security) - Juraj Somorovsky (Paderborn University) - Vladislav Mladenov (Ruhr University Bochum)
For more information
If you have any questions or comments about this advisory: Open an issue in pysaml2 Email us at the incident-response address
Other sources
PySAML2 is a pure python implementation of SAML Version 2 Standard. PySAML2 before 6.5.0 has an improper verification of cryptographic signature vulnerability. All users of pysaml2 that need to validate signed SAML documents are impacted. The vulnerability is a variant of XML Signature wrapping because it did not validate the SAML document against an XML schema. This allowed invalid XML documents to be processed and such a document can trick pysaml2 with a wrapped signature. This is fixed in PySAML2 6.5.0.
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2021-21238?
CVE-2021-21238 is considered to have a moderate severity level due to the potential for invalid SAML documents to bypass verification processes.
How do I fix CVE-2021-21238?
To fix CVE-2021-21238, upgrade to pysaml2 version 6.5.0 or later.
What does CVE-2021-21238 affect?
CVE-2021-21238 affects all users of pysaml2 who utilize the default CryptoBackendXmlSec1 backend for verifying signed SAML documents.
What is the main issue described in CVE-2021-21238?
The main issue in CVE-2021-21238 is the lack of validation against an XML schema for SAML documents in pysaml2 versions up to 6.4.1.
Can I still use pysaml2 if I'm affected by CVE-2021-21238?
While you can still use pysaml2 if affected by CVE-2021-21238, it is essential to upgrade to the secure version to avoid potential security risks.