CVE-2021-21238 SAML XML Signature wrapping

Medium 6.5 Published 21 Jan 2021 Updated 3 Aug 2024

Attackers can bypass SAML signature validation in PySAML2 by using XML signature wrapping, allowing unauthorized access to protected resources.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: Available

What is CVE-2021-21238?

CVE-2021-21238 is a medium-severity vulnerability in IdentityPython pysaml2, published on 21 Jan 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

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.

Weakness: CWE-347

Which versions are affected by CVE-2021-21238?

3 open source packages ship an affected version, including pysaml2. It affects 1 product.

Package	Affected	Fixed in
`pysaml2` PyPI	All versions	`6.5.0`
`pysaml2` PyPI	All versions	`6.5.0`
`pysaml2` PyPI	All versions	`6.5.0`

Products include Pysaml2 Project Pysaml2.

How do I fix CVE-2021-21238?

Upgrade pysaml2 to 6.5.0 or later.

Is CVE-2021-21238 being exploited?

There is no known exploitation of CVE-2021-21238 in the wild and no public exploit code.

Sources

Also known as DEBIAN-CVE-2021-21238, GHSA-f4g9-h89h-jgv9, PYSEC-2021-48, UBUNTU-CVE-2021-21238.