SAML XML Signature wrapping in PySAML2
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
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pysaml2 | < 6.5.0 | 6.5.0 |
References
- https://pypi.org/project/pysaml2
- https://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0
- https://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14
- https://github.com/IdentityPython/pysaml2/security/advisories/GHSA-f4g9-h89h-jgv9
- https://nvd.nist.gov/vuln/detail/CVE-2021-21238
- https://github.com/IdentityPython/pysaml2
- https://github.com/pypa/advisory-database/tree/main/vulns/pysaml2/PYSEC-2021-48.yaml
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N- Weakness (CWE)
CWE-347- Platform
- Python (PyPI)
- Package
pysaml2- Disclosed
- 21.01.2021
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-48 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-f4g9-h89h-jgv9 - CC BY 4.0
Vulnerability history: pysaml2
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 03.2017 01.2021
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 2
- High 2
- Medium 3
Disclosures per year
- 2017: 3
- 2018: 1
- 2019: 0
- 2020: 1
- 2021: 2
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 0
-
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