CVE-2026-78699 in ash_postgres
Summary
by MITRE • 08/30/2026
Unchecked Return Value vulnerability in ash-project ash_postgres allows a user who can drive a tenant rename to a name that collides with an existing tenant's schema to have their tenant record repointed at that other tenant's live schema, gaining access to its data.
AshPostgres.MultiTenancy.rename_tenant/3 issues the ALTER SCHEMA ... RENAME TO ... with the non-raising Ecto.Adapters.SQL.query/2, discards its {:ok, _} | {:error, _} result, and unconditionally returns :ok. PostgreSQL rejects the rename when the target schema already exists (and on insufficient privilege or lock timeout), but that failure never reaches the caller. The calling manage_tenant update action therefore sees success and commits the tenant row with the new name, which is the schema of a different existing tenant, so subsequent reads and writes for that tenant run against the other tenant's data.
This issue affects ash_postgres: from 0.25.0 before 2.13.0.
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Analysis
by VulDB Data Team • 08/30/2026
The vulnerability identified in AshPostgres represents a critical failure in error handling during multi-tenancy operations, specifically within the tenant renaming mechanism. This flaw allows an attacker who possesses the ability to initiate a tenant rename operation to exploit the lack of validation for database schema conflicts. The core technical issue lies in the implementation of the ash_postgres.MultiTenancy.rename_tenant/3 function, which interacts with PostgreSQL via Ecto.Adapters.SQL.query/2 using a non-raising query mode. This design choice means that if the underlying SQL command fails, such as when attempting to rename a schema to a name that already exists in the database, the error is silently discarded rather than propagated back to the application logic. Consequently, the function unconditionally returns an :ok status regardless of whether the database operation actually succeeded or failed due to constraint violations like duplicate schema names.
From a technical perspective, this behavior creates a dangerous state where the application layer believes the tenant rename was successful when it may have been rejected by PostgreSQL. When a user attempts to rename their tenant's schema to match an existing tenant's schema name, PostgreSQL correctly rejects the ALTER SCHEMA RENAME command because target schemas must be unique within a database. However, since AshPostgres ignores this error response and reports success, the subsequent manage_tenant update action proceeds to commit the change in the application's metadata layer. This results in the internal record for the attacker-controlled tenant being repointed to point at the schema of an existing, legitimate tenant. The disconnect between the database state and the application state is the root cause of this vulnerability, as the application continues to operate under the false assumption that the rename operation modified the intended resources.
The operational impact of this flaw is severe, leading directly to unauthorized data access and potential data integrity issues. Once the tenant record has been repointed to another tenant's schema, all subsequent read and write operations for the affected tenant are directed toward the victim tenant's live database schema. This effectively grants the attacker full administrative-like access to the other tenant's data without any authentication or authorization checks from AshPostgres itself, as the system trusts its own internal metadata mappings. An adversary can exfiltrate sensitive information belonging to another organization or user segment, violating confidentiality requirements and potentially leading to compliance violations under standards such as GDPR or HIPAA if personal health or financial data is involved. Furthermore, any writes performed by the attacker would corrupt the victim tenant's data, impacting availability and integrity.
This vulnerability aligns with CWE-252, Unchecked Return Value, where a function returns an indication of success or failure that is not properly checked before proceeding with subsequent operations. It also relates to CWE-697, Incorrect Comparison, in the sense that the application incorrectly assumes that returning :ok equates to a successful schema rename when it may only indicate that no exception was raised by the Ecto adapter. In terms of attack vectors and tactics, this flaw facilitates privilege escalation within the multi-tenancy context, allowing lateral movement between tenant boundaries which should be strictly isolated. It can be categorized under MITRE ATT&CK techniques related to Data Exfiltration over Alternative Protocol or Unauthorized Access to Functionality, as it bypasses intended access controls by manipulating internal state mappings rather than breaking cryptographic protections directly.
Mitigation strategies must focus on enforcing strict error handling and validation at the application layer before committing changes to metadata. Developers should modify the ash_postgres.MultiTenancy.rename_tenant/3 function to explicitly check the result of the SQL query for errors, ensuring that any failure from PostgreSQL is raised as an exception or returned as a clear error tuple rather than being discarded. Additionally, implementing pre-validation checks within the application logic can prevent attempts to rename schemas to names that are already in use by other tenants. This involves querying the database schema list prior to issuing the ALTER SCHEMA command and aborting the operation if a collision is detected. Upgrading ash_postgres to version 2.13.0 or later resolves this issue, as these versions include fixes for proper error propagation during tenant management operations. Until an upgrade is performed, administrators should review logs for failed SQL queries related to schema renames and restrict rename permissions to trusted internal services only where possible.