EUVD-2025-210492
GHSA-984h-wx22-r594
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Remote unauthenticated request against a live endpoint (AV:N/AC:L/PR:N/UI:N), but real impact is unauthorized developer-account creation, so C/I only Low and no availability impact.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
Lifecycle Timeline
4DescriptionCVE.org
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).
AnalysisAI
Cross-tenant self-service signup bypass in Microsoft Azure API Management (through 2025-10-17) lets remote unauthenticated actors register developer-portal accounts against a tenant where signup was disabled in the UI, by swapping the Host header or tenant identifier to reuse another tenant's still-live registration endpoint. Publicly available proof-of-concept exploit code exists (GHSA-vcwf-73jp-r7mv), but Microsoft evaluated the report and determined the behavior did not cross a security boundary, calling it a configuration/state issue rather than a product vulnerability affecting tenant isolation. No public in-the-wild exploitation has been identified, and the EPSS probability is low (0.18%, 7th percentile).
Technical ContextAI
Azure API Management (APIM) is Microsoft's managed API gateway and developer-portal platform used to publish, secure, and analyze APIs. It supports self-service signup where consumers create developer accounts using username/password Basic Authentication. The reported flaw is classified under CWE-284 (Improper Access Control): the developer-portal signup REST endpoint continues to accept and process registration requests based on the inbound Host header even after an administrator disables signup in the portal UI. Because UI-layer configuration does not propagate to an enforced check at the underlying API endpoint, a request re-pointed at a different tenant hostname (Tenant B) is still honored. Note the CPE data is a placeholder ('cpe:2.3:a:n/a:n/a:*') and provides no concrete version boundaries, consistent with a MITRE-reported, service-side SaaS issue rather than a versioned on-prem product.
RemediationAI
No vendor-released patch or fix version has been identified, and Microsoft has categorized the report as a configuration/state issue rather than a product vulnerability, so treat mitigation as a hardening exercise on the operator side. For APIM tenants that intend signup to be disabled, do not rely on the developer-portal UI toggle alone: disable Basic Authentication / username-password identity provider entirely for the tenant, and where signup is not needed remove or restrict the self-service registration path rather than merely hiding it. Front the developer portal with access controls that validate and constrain the Host header at the gateway or a fronting layer (e.g., Azure Front Door / WAF rules) so cross-tenant hostname reuse against the signup endpoint is blocked, and monitor developer-account creation events for unexpected registrations. Trade-offs: disabling Basic Auth or the identity provider will break any legitimate self-service onboarding that depends on it, and Host-header enforcement must be scoped carefully to avoid blocking valid custom-domain traffic. Track the vendor advisory and GHSA-vcwf-73jp-r7mv (https://github.com/bountyyfi/Azure-APIM-Cross-Tenant-Signup-Bypass/security/advisories/GHSA-vcwf-73jp-r7mv) and the NVD entry (https://nvd.nist.gov/vuln/detail/CVE-2025-66390) for any future Microsoft guidance.
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Same weakness CWE-284 – Improper Access Control
View allSame technique Authentication Bypass
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External POC / Exploit Code
Leaving vuln.today