CVE-2026-75509

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 6.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.1% (1st percentile of EPSS-scored CVEs). 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, secondary
Elevated
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.1%CVSS: 6.5Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to version 1.7.3, JWTClaimsRegistry applies membership matching to list-valued iss and sub claims, allowing an array-valued iss that contains the expected issuer to pass an intended equality check and enabling issuer-validation bypass. This issue is fixed in version 1.7.3.

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
45
EG Risk 45/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation40% × 40%
Automatability0% × 15%
CISA SSVC: Track at low or medium mission impact; Track* at high (mission-essential systems).
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.1%
EPSS %ILE
1st
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Track* at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

August 24, 2026

Last Modified

September 9, 2026

Advisory Details (2)

Auto-updated Aug 24, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github.
githubMentions a patch (unverified)🟡 PoC Available

joserfc accepts array-typed single-string claims (iss/sub/jti) , issuer-validation bypass · Advisory · authlib/joserfc · GitHub

https://github.com/authlib/joserfc/security/advisories/GHSA-r74j-q665-7rpj
github_commit Patch Available

commit 76ee6a59bf57 (authlib/joserfc)

Patch available: authlib/joserfc 1.7.3 (contains commit 76ee6a59bf57)

https://github.com/authlib/joserfc/commit/76ee6a59bf5773c0af00b99076c5e199031f97f1

Affected Packages

(2 across 2 ecosystems)
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
joserfc1.1.0-1 ... 1.7.4-1 (22 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
joserfc1.1.0-1 ... 1.7.2-1 (20 versions)
  • every version up to 1.7.3-1: fixed in 1.7.3-1
—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 12× in last 7d / 45× 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. 2026-10-10 20:00 UTCEPSS rescore
  2. 2026-10-10 12:30 UTCEG score recompute
  3. 2026-10-09 20:07 UTCEPSS rescore
  4. 2026-10-09 05:48 UTCEG score recompute
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  9. 2026-10-06 15:18 UTCEPSS rescore
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  11. 2026-10-05 17:43 UTCEPSS rescore
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  16. 2026-10-01 19:50 UTCEPSS rescore
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  19. 2026-09-29 15:24 UTCEPSS rescore
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  21. 2026-09-28 13:52 UTCEPSS rescore
  22. 2026-09-27 23:18 UTCEG score recompute
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  24. 2026-09-26 22:18 UTCEG score recompute
  25. 2026-09-26 15:59 UTCEPSS rescore
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  1. 2026-09-26 00:28 UTCEPSS rescore
  2. 2026-09-25 14:46 UTCEG score recompute
  3. 2026-09-24 14:04 UTCEPSS rescore
  4. 2026-09-24 12:46 UTCEG score recompute
  5. 2026-09-23 17:54 UTCEPSS rescore
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  7. 2026-09-22 16:01 UTCEPSS rescore
  8. 2026-09-19 06:28 UTCEG score recompute
  9. 2026-09-18 19:28 UTCEPSS rescore
  10. 2026-09-18 05:27 UTCEG score recompute
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  12. 2026-09-16 14:08 UTCEPSS rescore
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  15. 2026-09-15 03:12 UTCEPSS rescore
  16. 2026-09-14 01:23 UTCEG score recompute
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  18. 2026-09-12 15:02 UTCEPSS rescore
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  20. 2026-09-11 14:53 UTCEPSS rescore
  21. 2026-09-10 22:17 UTCEG score recompute
  22. 2026-09-10 09:35 UTCEPSS rescore
  23. 2026-09-09 01:21 UTCEG score recompute
  24. 2026-09-08 22:01 UTCEPSS rescore
  25. 2026-09-07 10:18 UTCEG score recompute
  26. 2026-09-06 13:48 UTCEPSS rescore
  27. 2026-09-06 09:16 UTCEG score recompute
  28. 2026-09-04 07:10 UTCEG score recompute
  29. 2026-09-04 05:07 UTCEPSS rescore
  30. 2026-09-03 05:59 UTCEG score recompute
  31. 2026-09-02 14:12 UTCEPSS rescore
  32. 2026-09-02 04:59 UTCEG score recompute
  33. 2026-09-01 13:54 UTCEPSS rescore
  34. 2026-08-29 00:21 UTCEG score recompute
  35. 2026-08-28 21:42 UTCEPSS rescore
  36. 2026-08-27 19:25 UTCEG score recompute
  37. 2026-08-27 14:25 UTCEPSS rescore
  38. 2026-08-26 18:26 UTCEG score recompute
  39. 2026-08-26 14:47 UTCEPSS rescore
  40. 2026-08-25 17:25 UTCEG score recompute
  41. 2026-08-25 17:01 UTCEG score recompute
  42. 2026-08-25 13:49 UTCEPSS rescore
  43. 2026-08-24 20:25 UTCEG score recompute
  44. 2026-08-24 20:11 UTCEG score recompute
  45. 2026-08-24 20:11 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-75509?
CVE-2026-75509 is a medium vulnerability published on August 24, 2026. joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to version 1.7.3, JWTClaimsRegistry applies membership matching to list-valued iss and sub claims, allowing an array-valued iss that contains the expected issuer to pass…
When was CVE-2026-75509 disclosed?
CVE-2026-75509 was first published on August 24, 2026, with the most recent update on September 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-75509 actively exploited?
CVE-2026-75509 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.1% probability of exploitation in the next 30 days (1st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-75509?
CVE-2026-75509 has a CVSS base score of 6.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-75509?
A fix for CVE-2026-75509 is available: update to the fixed version the vendor names in its advisory.

Dependency Blast Radius

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