Improper Verification of Cryptographic Signature in Python implementation of SAML2

1) Improper Verification of Cryptographic Signature

EUVDB-ID: #VU50366

Risk: Medium

CVSSv3.1: 5.7 [CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N/E:U/RL:O/RC:C]

CVE-ID: CVE-2021-21238

CWE-ID: CWE-347 - Improper Verification of Cryptographic Signature

Exploit availability: No

Description

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. 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.

Mitigation

Install update from vendor's website.

Vulnerable software versions

Python implementation of SAML2: 6.0.0 - 6.4.1

External links

http://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14
http://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0
http://github.com/IdentityPython/pysaml2/security/advisories/GHSA-f4g9-h89h-jgv9
http://pypi.org/project/pysaml2

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.