{"id":"CVE-2025-66390","title":"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 …","summary":"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 …","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cwe":["CWE-284"],"published":"2026-07-21","updated":"2026-10-05","sourceUpdated":"2026-10-05T18:10:00.200","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2025-66390","references":[{"url":"https://github.com/bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass","label":"cve@mitre.org"},{"url":"https://github.com/bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass/security/advisories/GHSA-vcwf-73jp-r7mv","label":"cve@mitre.org"},{"url":"https://github.com/bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass","label":"134c704f-9b21-4f2e-91b3-4a467353bcc0"}],"tags":["nvd","exploit-available"],"epss":0.00642,"epssPercentile":0.48996,"exploits":{"github":1,"githubRepos":["https://github.com/dz-y/Azure-APIM-Dev-Portal-Signup-Bypass"],"checkedAt":"2026-10-05T18:29:46.182Z"},"exploitAvailable":true,"ingestedAt":"2026-10-05T18:29:11.174Z","slug":"CVE-2025-66390","body":"## Overview\n\nIn 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).\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"abyssal","depthScore":66,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[]}