CVE-2021-21238: Pysaml2 SAML XML Signature Wrapping Vulnerability

MODERATE
Advisory Identifier: GHSA-f4g9-h89h-jgv9
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CVSS 6.5
CWE-347
Published
Advisory Summary

CVE-2021-21238 is a MODERATE (CVSS 6.5) saml xml signature wrapping vulnerability (CWE-347: Improper Verification of Cryptographic Signature) affecting Pysaml2 libraries in the PyPI ecosystem. The issue involves saml xml signature wrapping in pysaml2. Remediation is available by upgrading affected packages to version 6.5.0.

CVE-2021-21238 at a Glance

CVE Identifier CVE-2021-21238
GHSA Identifier GHSA-f4g9-h89h-jgv9
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-347: Improper Verification of Cryptographic Signature
Affected Product Pysaml2
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 6.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2021-21238

To remediate this vulnerability, upgrade all affected Pysaml2 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

pysaml2 fixed: 6.5.0 
pip install pysaml2>=6.5.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show pysaml2

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2021-21238, inspect your installed packages using pip:

pip show pysaml2

Analyze the terminal output to locate any version of Pysaml2 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.5.0), your application is affected.

Note: The pip show pysaml2 command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-347: Improper Verification of Cryptographic Signature, where the product does not verify, or incorrectly verifies, the cryptographic signature for data. In Pysaml2, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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)

CVE-2021-21238 Affected Pysaml2 Versions

1 component(s)
Fixed Versions:
6.5.0
Product / Package Ecosystem Affected Versions Fixed Version
pysaml2
pypi/pysaml2
PyPI
< 6.5.0
6.5.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/IdentityPython/pysaml2/security/advisories/GHSA-f4g9-h89h-jgv9
NVD — CVE-2021-21238 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-21238
Security Fix Commit FIX COMMIT
https://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14
Pysaml2 Source Repository REPOSITORY
https://github.com/IdentityPython/pysaml2
Pysaml2 Release RELEASE
https://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0
Pysaml2 Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/pysaml2/PYSEC-2021-48.yaml
pypi.org/project/pysaml2 WEB
https://pypi.org/project/pysaml2

Frequently Asked Questions

What is CVE-2021-21238?
CVE-2021-21238 is a security vulnerability in Pysaml2 involving SAML XML Signature wrapping in PySAML2 under CWE-347: Improper Verification of Cryptographic Signature.
Which Pysaml2 versions are affected?
Affected versions include releases prior to 6.5.0 across affected packages: pysaml2.
What version fixes CVE-2021-21238?
Upgrading to 6.5.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is pysaml2 affected?
Yes, pysaml2 is affected in releases prior to 6.5.0. Upgrade your dependency to 6.5.0 or later.
What is the CVSS score of CVE-2021-21238?
CVE-2021-21238 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2021-21238?
CVE-2021-21238 is classified under CWE-347: Improper Verification of Cryptographic Signature (The product does not verify, or incorrectly verifies, the cryptographic signature for data.).
How can I check PyPI dependencies for CVE-2021-21238?
Run the dependency tree command: 'pip show pysaml2'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f4g9-h89h-jgv9",
  "modified" : "2024-10-14T15:50:30Z",
  "published" : "2021-01-21T14:12:16Z",
  "aliases" : [ "CVE-2021-21238" ],
  "summary" : "SAML XML Signature wrapping in PySAML2",
  "details" : "### Impact\n\nAll 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.\n\n### Patches\n\nUsers should upgrade to pysaml2 `v6.5.0`.\n\n### Workarounds\n\nNo workaround provided at this point.\n\n### References\n\nNo references provided at this point.\n\n### Credits\n\n- Victor Schönfelder Garcia (isits AG International School of IT Security)\n- Juraj Somorovsky (Paderborn University)\n- Vladislav Mladenov (Ruhr University Bochum)\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n* Open an issue in [pysaml2](https://github.com/IdentityPython/pysaml2)\n* Email us at [the incident-response address](mailto:incident-response@idpy.org)",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "pysaml2"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.5.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/IdentityPython/pysaml2/security/advisories/GHSA-f4g9-h89h-jgv9"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-21238"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/IdentityPython/pysaml2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/pysaml2/PYSEC-2021-48.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://pypi.org/project/pysaml2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-347" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2021-01-21T14:11:38Z",
    "nvd_published_at" : "2021-01-21T15:15:00Z"
  }
}