CVE-2025-66390

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-07-21. CISA-ADP (Vulnrichment) CVSS v3.1 baseline 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cisa-adp, epss, ghsa
Trending — 3 sources updated this weekElevated
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.8Exploit: Elevated riskExposed: 0

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

In Microsoft Azure API Management through 2025-10-17, when self-service signup (username/password Basic Authentication) is enabled in Tenant A, an attacker can reuse the registration flow by changing the hostname or tenant identifier to Tenant B, even when Tenant B has signup disabled at the UI level. In other words, disabling signup in the UI does not disable the underlying API endpoint (which still accepts cross-tenant requests based on the Host header). NOTE: The supplier states that they evaluated the report and determined it did not cross a security boundary (i.e., the observed behavior was a configuration/state issue rather than an exploitable product vulnerability affecting tenant isolation). NOTE: The supplier evaluated this report and determined that it did not cross a security boundary (i.e., the observed behavior was a configuration/state issue rather than an exploitable product vulnerability affecting tenant isolation).

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
75(Attend)
EG Risk 75/100SSVC: Attend

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
Severity98% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
27%
KEV
Not listed

Published

July 21, 2026

Last Modified

July 23, 2026

Advisory Details (2)

Auto-updated Jul 25, 2026
Patch available. Sources: github.
generic

GitHub - bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass: Security advisory: Azure APIM Developer Portal allows cross-tenant account registration by bypassing UI signup restrictions. Reported to MSRC twice - closed as "by design". · GitHub

https://github.com/bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass
github Patch Available

Azure APIM Cross-Tenant Signup Bypass · Advisory · bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass · GitHub

https://github.com/bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass/security/advisories/GHSA-vcwf-73jp-r7mv

Vendor Advisories for CVE-2025-66390(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 43× in last 7d / 55× 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. 2026-07-30 15:58 UTCGHSA enrichment
  2. 2026-07-30 11:58 UTCEG score recompute
  3. 2026-07-30 11:58 UTCGHSA enrichment
  4. 2026-07-30 08:01 UTCGHSA enrichment
  5. 2026-07-30 03:30 UTCEG score recompute
  6. 2026-07-30 03:30 UTCGHSA enrichment
  7. 2026-07-30 01:30 UTCEPSS rescore
  8. 2026-07-29 23:44 UTCGHSA enrichment
  9. 2026-07-29 19:56 UTCGHSA enrichment
  10. 2026-07-29 15:36 UTCGHSA enrichment
  11. 2026-07-29 11:51 UTCGHSA enrichment
  12. 2026-07-29 08:05 UTCGHSA enrichment
  13. 2026-07-29 04:20 UTCGHSA enrichment
  14. 2026-07-29 00:34 UTCGHSA enrichment
  15. 2026-07-28 20:49 UTCGHSA enrichment
  16. 2026-07-28 17:03 UTCEG score recompute
  17. 2026-07-28 17:03 UTCGHSA enrichment
  18. 2026-07-28 15:35 UTCEPSS rescore
  19. 2026-07-28 11:52 UTCGHSA enrichment
  20. 2026-07-28 08:04 UTCGHSA enrichment
  21. 2026-07-28 04:19 UTCGHSA enrichment
  22. 2026-07-28 00:34 UTCGHSA enrichment
  23. 2026-07-27 20:49 UTCGHSA enrichment
  24. 2026-07-27 17:00 UTCEG score recompute
  25. 2026-07-27 17:00 UTCGHSA enrichment
Show 30 more
  1. 2026-07-27 14:12 UTCEPSS rescore
  2. 2026-07-27 13:14 UTCGHSA enrichment
  3. 2026-07-27 09:29 UTCGHSA enrichment
  4. 2026-07-27 05:44 UTCGHSA enrichment
  5. 2026-07-27 01:58 UTCGHSA enrichment
  6. 2026-07-26 22:11 UTCGHSA enrichment
  7. 2026-07-26 18:26 UTCEG score recompute
  8. 2026-07-26 18:26 UTCGHSA enrichment
  9. 2026-07-26 14:54 UTCEPSS rescore
  10. 2026-07-26 14:54 UTCEPSS rescore
  11. 2026-07-26 14:30 UTCGHSA enrichment
  12. 2026-07-26 10:44 UTCEG score recompute
  13. 2026-07-26 10:44 UTCGHSA enrichment
  14. 2026-07-26 04:25 UTCEG score recompute
  15. 2026-07-26 04:24 UTCGHSA enrichment
  16. 2026-07-25 14:17 UTCEPSS rescore
  17. 2026-07-24 14:17 UTCEPSS rescore
  18. 2026-07-24 14:17 UTCEPSS rescore
  19. 2026-07-23 14:18 UTCEPSS rescore
  20. 2026-07-23 14:18 UTCEPSS rescore
  21. 2026-07-23 03:01 UTCEG score recompute
  22. 2026-07-22 23:25 UTCEG score recompute
  23. 2026-07-22 23:24 UTCGHSA enrichment
  24. 2026-07-22 16:03 UTCEG score recompute▲ 9.80
  25. 2026-07-22 16:03 UTCGHSA enrichment
  26. 2026-07-22 16:00 UTCMITRE cvelistV5CVSS v3 → 9.8 · severity → CRITICAL
  27. 2026-07-22 14:08 UTCEPSS rescore
  28. 2026-07-21 14:51 UTCNVD update
  29. 2026-07-21 14:00 UTCEG score recompute
  30. 2026-07-21 13:57 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2025-66390?
CVE-2025-66390 is a critical vulnerability published on July 21, 2026. In Microsoft Azure API Management through 2025-10-17, when self-service signup (username/password Basic Authentication) is enabled in Tenant A, an attacker can reuse the registration flow by changing the hostname or tenant identifier to Tenant B, even when Tenant B has signup disabled at the UI…
When was CVE-2025-66390 disclosed?
CVE-2025-66390 was first published in the National Vulnerability Database on July 21, 2026, with the most recent update on July 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2025-66390 actively exploited?
CVE-2025-66390 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 72.8% of all scored CVEs.
What is the CVSS score of CVE-2025-66390?
CVE-2025-66390 has a CVSS v3.1 base score of 9.8 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending).
How do I remediate CVE-2025-66390?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2025-66390, 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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