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CVE-2026-85787 - An incomplete list of disallowed inputs in the SQL validation component in Amazon awslabs postgres-mcp-server to modify data beyond the read-only scope

Bulletin ID: 2026-101-AWS
Scope: AWS
Content Type: Important (requires attention)
Publication Date: 09/04/2026 13:00 PM PDT

Description:

We have identified CVE-2026-85787, an incomplete list of disallowed inputs in the SQL validation component in Amazon awslabs postgres-mcp-server before version 1.1.7 might allow an unauthenticated actor to modify data beyond the read-only scope by placing crafted SQL into the content that is submitted when an authenticated user interacts with the MCP server.

Impacted versions: any pypi package version < 1.1.7

Resolution:

This issue has been addressed in version 1.1.7. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.

Workarounds:

Run the MCP server as a minimal-privilege Postgres role

The strongest control is to connect the MCP server using a dedicated Postgres role that has only the privileges it actually needs, so that the database itself enforces the boundary regardless of what SQL reaches it. In particular:

  • Do not connect as a superuser, rds_superuser, or the cluster master user. Those roles bypass row-level security, can read credential catalogs (pg_authid, pg_user_mappings), and can terminate other sessions.
  • For read-only use, grant only CONNECT + USAGE + SELECT on the schemas the agent needs, and force read-only transactions at the role level.
  • For read/write use, grant only the specific INSERT/UPDATE/DELETE privileges required, scoped to the necessary schemas and tables.

Combining a minimal-privilege role (database-enforced) with the blocklist (application-enforced) gives you defense in depth: even if a query slips past the blocklist, the role's privileges still bound what it can do.

References:

Acknowledgement:

We would like to thank Ashwak N for reporting this issue and working with us as part of our coordinated issue disclosure process.


Please email aws-security@amazon.com with any security questions or concerns.