CVE-2021-21239: Open default xmlsec1 key-type preference

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-01-21 · updated 2026-06-17
Weakness: CWE-347

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. 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 products

Debian Linux: 9.0
IdentityPython pysaml2: before 6.5.0 — fixed in 6.5.0

How to fix

Upgrade to a fixed version: IdentityPython pysaml2 6.5.0. Check the vendor advisory for mitigations.

References

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