---
id: CVE-2021-21238
aliases:
  - GHSA-f4g9-h89h-jgv9
  - PYSEC-2021-48
title: SAML XML Signature wrapping in PySAML2
summary: SAML XML Signature wrapping in PySAML2
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N'
vendor: pysaml2
product: pysaml2
ecosystem: pip
affected:
  - pysaml2 < 6.5.0
patched:
  - pysaml2 6.5.0
published: '2021-01-21'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:49:13.856780354Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-f4g9-h89h-jgv9'
references:
  - url: >-
      https://github.com/IdentityPython/pysaml2/security/advisories/GHSA-f4g9-h89h-jgv9
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-21238'
  - url: >-
      https://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14
  - url: 'https://github.com/IdentityPython/pysaml2'
  - url: 'https://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0'
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/pysaml2/PYSEC-2021-48.yaml
  - url: 'https://pypi.org/project/pysaml2'
tags:
  - osv
  - pip
epss: 0.01078
epssPercentile: 0.63601
ingestedAt: '2026-09-12T03:13:01.690Z'
---

## Overview

### 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](https://github.com/IdentityPython/pysaml2)
* Email us at [the incident-response address](mailto:incident-response@idpy.org)

## Affected packages

- `pysaml2 < 6.5.0`

## Remediation

Upgrade to a patched release:

- `pysaml2 6.5.0`