Affects Microsoft Azure API Management, a widely used cloud service; cross-tenant account creation can impact many organizations and warrants broad notification.
CVE-2025-66390
Host-header authentication bypass lets signup in Tenant A create accounts in Tenant B.
Is CVE-2025-66390 being exploited?
Not confirmed. CVE-2025-66390 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.64% probability of exploitation in the next 30 days.
How severe is CVE-2025-66390?
CVE-2025-66390 is rated Critical with a CVSS score of 9.8. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2025-66390?
Yes. A fix has been recorded for CVE-2025-66390. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2025-66390 affect?
CVE-2025-66390 affects Microsoft Azure API Management (through 2025-10-17), Azure APIM. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2025-66390?
Apply vendor patch when available; disable self-service signup at API layer; validate Host headers.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote attacker can create accounts in another tenant by altering Host header, bypassing UI-disabled signup and enabling unauthorized tenant enrollment and account access.
Immediate action required