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%, top 99% 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, 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%CVSS: 6.5Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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
6.5(medium)
EG Risk
45(Track)
EG Risk 45/100SSVC: Track

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%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
1%
KEV
Not listed

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.
github Patch Available🟡 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 rangeFixed inDependents
joserfc1.1.0-1 ... 1.7.4-1 (22 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
joserfc1.1.0-1 ... 1.7.2-1 (20 versions)1.7.3-1—

Weakness Classification(2)

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

Data Freshness Timeline

(refreshed 10× in last 7d / 38× 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. 2026-09-19 06:28 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 05:27 UTCEG score recompute
  4. 2026-09-17 04:27 UTCEG score recompute
  5. 2026-09-16 14:08 UTCEPSS rescore
  6. 2026-09-16 05:15 UTCEPSS rescore
  7. 2026-09-16 03:27 UTCEG score recompute
  8. 2026-09-15 03:12 UTCEPSS rescore
  9. 2026-09-14 01:23 UTCEG score recompute
  10. 2026-09-13 00:24 UTCEG score recompute
  11. 2026-09-12 15:02 UTCEPSS rescore
  12. 2026-09-11 23:24 UTCEG score recompute
  13. 2026-09-11 14:53 UTCEPSS rescore
  14. 2026-09-10 22:17 UTCEG score recompute
  15. 2026-09-10 09:35 UTCEPSS rescore
  16. 2026-09-09 01:21 UTCEG score recompute
  17. 2026-09-08 22:01 UTCEPSS rescore
  18. 2026-09-07 10:18 UTCEG score recompute
  19. 2026-09-06 13:48 UTCEPSS rescore
  20. 2026-09-06 09:16 UTCEG score recompute
  21. 2026-09-04 07:10 UTCEG score recompute
  22. 2026-09-04 05:07 UTCEPSS rescore
  23. 2026-09-03 05:59 UTCEG score recompute
  24. 2026-09-02 14:12 UTCEPSS rescore
  25. 2026-09-02 04:59 UTCEG score recompute
Show 13 more
  1. 2026-09-01 13:54 UTCEPSS rescore
  2. 2026-08-29 00:21 UTCEG score recompute
  3. 2026-08-28 21:42 UTCEPSS rescore
  4. 2026-08-27 19:25 UTCEG score recompute
  5. 2026-08-27 14:25 UTCEPSS rescore
  6. 2026-08-26 18:26 UTCEG score recompute
  7. 2026-08-26 14:47 UTCEPSS rescore
  8. 2026-08-25 17:25 UTCEG score recompute
  9. 2026-08-25 17:01 UTCEG score recompute
  10. 2026-08-25 13:49 UTCEPSS rescore
  11. 2026-08-24 20:25 UTCEG score recompute
  12. 2026-08-24 20:11 UTCEG score recompute
  13. 2026-08-24 20:11 UTCMITRE cvelistV5first tracked

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 in the National Vulnerability Database 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% probability of exploitation in the next 30 days, which ranks it in the top 99.4% of all scored CVEs.
What is the CVSS score of CVE-2026-75509?
CVE-2026-75509 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-75509?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-75509, 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-75509

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