What’s Vulnerable › Vulnerabilities

CVE-2025-66390

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-21 · updated 2026-10-12
• Weakness: CWE-284

Description

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).

References

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

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