{"id":"CVE-2021-21238","aliases":["GHSA-f4g9-h89h-jgv9","PYSEC-2021-48"],"url":"https://o3.security/vulnerability/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)","published":"2021-01-21T15:15:14.110Z","modified":"2026-10-24T10:50:23.478478440Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"pysaml2","fixedVersion":"6.5.0"}],"fix":{"url":"https://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14","label":"IdentityPython/pysaml2@1d8fd26"},"references":[{"type":"ADVISORY","url":"https://github.com/IdentityPython/pysaml2/releases/tag/v6.5.0"},{"type":"ADVISORY","url":"https://github.com/IdentityPython/pysaml2/security/advisories/GHSA-f4g9-h89h-jgv9"},{"type":"FIX","url":"https://github.com/IdentityPython/pysaml2/commit/1d8fd268f5bf887480a403a7a5ef8f048157cc14"},{"type":"PACKAGE","url":"https://pypi.org/project/pysaml2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-21238"},{"type":"PACKAGE","url":"https://github.com/IdentityPython/pysaml2"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/pysaml2/PYSEC-2021-48.yaml"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-24T10:50:23.478478440Z"}}