CVE-2025-66390Public exploitNetwork attack vector

Cross-tenant account creation via Host-routed signup

Published Jul 21, 2026 · Updated Jul 21, 2026

Improper access control in Microsoft Azure API Management through 2025-10-17 allows remote attackers to create cross-tenant accounts. The Developer Portal /signup endpoint routes a crafted POST by its Host header and stays active when the signup UI is disabled. Basic Authentication and a network-accessible Developer Portal are required; Microsoft states that the behavior does not cross a tenant-isolation security boundary.

CVSS severity9.8
Critical
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Microsoft Azure API Management through 2025-10-17 allows remote attackers to create cross-tenant accounts. The Developer Portal /signup endpoint routes a crafted POST by its Host header and stays active when the signup UI is disabled. Basic Authentication and a network-accessible Developer Portal are required; Microsoft states that the behavior does not cross a tenant-isolation security boundary.

The record

CVE
CVE-2025-66390
Published
Jul 21, 2026
Updated
Jul 21, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-284, T1136.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 21, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-284Improper Access Control
T1136.003Create Account: Cloud Account

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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