Improper Verification of Cryptographic Signature in Python implementation of SAML2 - CVE-2021-21239

Vulnerability details

The vulnerability allows a remote non-authenticated attacker to manipulate data.

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.

Affected software

How to mitigate CVE-2021-21239

Links to Public Exploits and PoC-codes

• Exploit #10229 - CVE-2021-21239-Exploit (Report documentation of this script is below) (July 19, 2024)

External References

• https://github.com/IdentityPython/pysaml2/commit/46578df0695269a16f1c94171f1429873f90ed99
• https://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0
• https://github.com/IdentityPython/pysaml2/security/advisories/GHSA-5p3x-r448-pc62
• https://pypi.org/project/pysaml2
• https://www.aleksey.com/pipermail/xmlsec/2013/009717.html

Related Security Bulletins

• Improper Verification of Cryptographic Signature in Python implementation of SAML2
• Improper Verification of Cryptographic Signature in py3-saml2 (Alpine package)
• Ubuntu update for python-pysaml2
• Ubuntu update for python-pysaml2