CVE-2026-56223: Capgo - Account Takeover via Cross-Domain SSO Email Assertion in provision-user

Synopsis

This is an authentication-bypass and account-takeover vulnerability in Capgo, affecting the provision-user endpoint used during enterprise single sign-on (SSO) flows. An attacker who controls an enterprise org admin account and a malicious identity provider (IdP) can craft SAML assertions (the XML tokens an IdP sends to assert a user's identity) containing a victim's email address; because the provision-user endpoint matches accounts by email without verifying that the SSO provider is authorized for that email domain, the merge succeeds and the attacker gains full access to the victim account, its organizations, and its data. Exploitation requires network access and an existing high-privilege (org admin) account but no victim interaction. A patched-image rebuild at version 12.128.2 is available on HarborGuard for environments running an affected version.

HarborGuard Coverage

Exploit Conditions

• Network reachabilityRequired

  The attacker must reach the Capgo provision-user endpoint over the network; the CVSS vector records AV:N, meaning the vulnerable surface is exposed to network-accessible requests.

• AuthenticationRequired

  The attacker must hold an enterprise org admin account (CVSS PR:H); any lower-privilege account is not sufficient to trigger the vulnerable SSO provisioning flow.

• Victim interactionNot required

  No action by the victim is needed; the account merge is triggered entirely server-side when the attacker submits the forged SAML assertion (CVSS UI:N).

• Attack complexityDetail

  Attack complexity is low (CVSS AC:L); the exploit is reliable and does not depend on race conditions, memory layout, or other environmental factors beyond holding org admin credentials and controlling a malicious IdP.

Blast Radius

• Reads all data stored in the victim account, including application configurations, API keys, and any secrets stored within associated Capgo organizations.
• Gains write access to victim-owned organizations and their settings, allowing modification or deletion of deployments, channels, and access controls.
• Takes over organizational memberships and can invite or remove members, effectively locking the legitimate owner out of their organization.
• Propagates access to any downstream systems or integrations that trust Capgo organization membership or API credentials.