CVE-2021-21239

MEDIUMNVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under NVD CVSS v3. EPSS exploit probability: 0.7%, top 28% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
6.5
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 1%CVSS: 6.5Exploit: NoneExposed: 0

A fix is available — apply it.

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.

CVSS v3
6.5
EG Score
6.5(medium)
EPSS
64.0%
KEV
Not listed

Published

January 21, 2021

Last Modified

November 21, 2024

References (12)

Patch Availability(2)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntupython3-pysaml2 (4.9.0-0ubuntu3.1) @ focal2026-05-26ubuntu
ubuntupython3-pysaml2 (3.0.0-3ubuntu1.16.04.4+esm1) @ xenial2026-05-26ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFixed inDependents
pysaml20.4.3 ... 6.4.1 (45 versions)6.5.0—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(2)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 9× in last 7d / 48× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-12 05:44 UTCEPSS rescore
  2. 2026-07-12 05:44 UTCEPSS rescore
  3. 2026-07-11 08:25 UTCEPSS rescore
  4. 2026-07-09 19:07 UTCEPSS rescore
  5. 2026-07-08 15:12 UTCEPSS rescore
  6. 2026-07-07 13:43 UTCEPSS rescore
  7. 2026-07-06 16:25 UTCEPSS rescore
  8. 2026-07-06 02:21 UTCEPSS rescore
  9. 2026-07-06 02:21 UTCEPSS rescore
  10. 2026-07-05 02:28 UTCEPSS rescore
  11. 2026-07-05 02:28 UTCEPSS rescore
  12. 2026-07-04 06:29 UTCEPSS rescore
  13. 2026-07-04 06:29 UTCEPSS rescore
  14. 2026-07-02 16:57 UTCEPSS rescore
  15. 2026-07-01 15:03 UTCEPSS rescore
  16. 2026-07-01 10:18 UTCOSV refresh
  17. 2026-06-30 23:20 UTCEPSS rescore
  18. 2026-06-30 23:20 UTCEPSS rescore
  19. 2026-06-29 14:04 UTCEPSS rescore
  20. 2026-06-29 14:04 UTCEPSS rescore
  21. 2026-06-28 04:54 UTCEPSS rescore
  22. 2026-06-28 04:54 UTCEPSS rescore
  23. 2026-06-27 03:06 UTCEPSS rescore
  24. 2026-06-27 03:06 UTCEPSS rescore
  25. 2026-06-25 13:48 UTCEPSS rescore
Show 59 more
  1. 2026-06-25 13:48 UTCEPSS rescore
  2. 2026-06-24 14:03 UTCEPSS rescore
  3. 2026-06-24 14:03 UTCEPSS rescore
  4. 2026-06-23 21:31 UTCEPSS rescore
  5. 2026-06-23 21:31 UTCEPSS rescore
  6. 2026-06-22 14:24 UTCEPSS rescore
  7. 2026-06-22 14:23 UTCEPSS rescore
  8. 2026-06-21 14:54 UTCEPSS rescore
  9. 2026-06-21 14:54 UTCEPSS rescore
  10. 2026-06-21 01:58 UTCEPSS rescore
  11. 2026-06-21 01:57 UTCEPSS rescore
  12. 2026-06-19 19:24 UTCEPSS rescore
  13. 2026-06-19 19:24 UTCEPSS rescore
  14. 2026-06-18 17:51 UTCEPSS rescore
  15. 2026-06-18 17:51 UTCEPSS rescore
  16. 2026-06-17 17:51 UTCEPSS rescore
  17. 2026-06-16 17:50 UTCEPSS rescore
  18. 2026-06-15 17:46 UTCEPSS rescore
  19. 2026-06-14 23:15 UTCEPSS rescore
  20. 2026-06-13 22:58 UTCEPSS rescore
  21. 2026-06-13 15:43 UTCOSV refresh
  22. 2026-06-12 23:10 UTCEPSS rescore
  23. 2026-06-12 23:10 UTCEPSS rescore
  24. 2026-06-11 13:58 UTCEPSS rescore
  25. 2026-06-10 22:16 UTCEPSS rescore
  26. 2026-06-10 22:16 UTCEPSS rescore
  27. 2026-06-10 13:20 UTCEPSS rescore
  28. 2026-06-08 14:15 UTCEPSS rescore
  29. 2026-06-08 14:15 UTCEPSS rescore
  30. 2026-06-07 15:23 UTCEPSS rescore
  31. 2026-06-07 15:23 UTCEPSS rescore
  32. 2026-06-06 13:46 UTCEPSS rescore
  33. 2026-06-06 13:46 UTCEPSS rescore
  34. 2026-06-06 13:46 UTCEPSS rescore
  35. 2026-06-05 22:45 UTCEPSS rescore
  36. 2026-06-05 22:45 UTCEPSS rescore
  37. 2026-06-05 06:09 UTCEPSS rescore
  38. 2026-06-05 06:09 UTCEPSS rescore
  39. 2026-06-05 06:08 UTCEPSS rescore
  40. 2026-06-04 13:10 UTCEPSS rescore
  41. 2026-06-02 20:11 UTCEPSS rescore
  42. 2026-06-02 20:11 UTCEPSS rescore
  43. 2026-06-01 13:50 UTCEPSS rescore
  44. 2026-06-01 13:50 UTCEPSS rescore
  45. 2026-05-31 22:29 UTCEPSS rescore
  46. 2026-05-31 22:29 UTCEPSS rescore
  47. 2026-05-31 00:15 UTCEPSS rescore
  48. 2026-05-31 00:15 UTCEPSS rescore
  49. 2026-05-29 13:42 UTCEPSS rescore
  50. 2026-05-28 13:43 UTCEPSS rescore
  51. 2026-05-28 13:43 UTCEPSS rescore
  52. 2026-05-27 13:39 UTCEPSS rescore
  53. 2026-05-26 21:43 UTCEG score recompute
  54. 2026-05-26 21:43 UTCVendor advisory
  55. 2026-05-26 13:42 UTCEPSS rescore
  56. 2026-05-26 13:42 UTCEPSS rescore
  57. 2026-05-26 07:17 UTCEPSS rescore
  58. 2026-05-26 07:17 UTCEPSS rescore
  59. 2026-05-24 16:49 UTCEPSS rescore

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-21239?
CVE-2021-21239 is a medium vulnerability published on January 21, 2021. 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…
When was CVE-2021-21239 disclosed?
CVE-2021-21239 was first published in the National Vulnerability Database on January 21, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-21239 actively exploited?
CVE-2021-21239 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 64.0% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-21239?
CVE-2021-21239 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2021-21239?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-21239, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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