Description

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. To remediate this issue, users should upgrade to version 1.1.7 or above.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.5",
  "pubDate": "2026-09-04T21:17:27.057Z",
  "pubdate": "2026-09-04T21:17:27.057Z",
  "executiveSummary": "The Amazon awslabs postgres-mcp-server, in versions prior to 1.1.7, contains a critical security flaw in its SQL validation component. The vulnerability is classified as an improper input validation issue, which enables a form of SQL injection. This flaw allows an unauthenticated actor to bypass intended read-only access controls by submitting malicious, crafted SQL payloads.\nWhen an authenticated user interacts with the compromised MCP server, the server processes the attacker's injected SQL, effectively escalating the attacker's privileges beyond the constrained scope. This allows unauthorized data modification, posing a severe risk to data integrity and system security. The vulnerability highlights a failure in the input sanitization mechanism, which is responsible for filtering out prohibited SQL commands before execution. Successful exploitation results in the ability for an external party to manipulate database contents through an indirect interaction with a legitimate, authenticated session, thereby undermining the security posture of the application's database abstraction layer.",
  "technicalDetails": "The vulnerability stems from an incomplete blacklist or insufficient filtering logic within the SQL validation component of the postgres-mcp-server. The component is designed to enforce a read-only security boundary, intended to prevent any data-modifying operations (such as UPDATE, DELETE, or INSERT) from being executed. However, the validation mechanism fails to account for a wide range of crafted SQL sequences, allowing malicious queries to pass through to the database backend.\nThe attack flow operates by leveraging the interaction between an unauthenticated actor and an authenticated user within the MCP framework. Since the validation layer does not correctly sanitize input before passing it to the SQL engine, an attacker can embed non-read-only SQL statements within the content processed by the server. When the authenticated user initiates a request that includes the attacker's crafted payload, the server fails to detect the malicious nature of the statement. Consequently, the database interprets the payload as part of the authorized workflow, executing the unauthorized commands with the privileges assigned to the MCP server's service account.\nThe root cause is a deficiency in the input validation component, which relies on a restrictive but incomplete set of rules rather than a robust, whitelist-based sanitization or a parameterized query approach that strictly separates code from data. Because the system improperly validates incoming content before execution, it is susceptible to various SQL injection vectors that can subvert the intended read-only constraints.\nThe impact of this vulnerability is significant, as it enables unauthorized data modification. By injecting crafted SQL, an actor can alter sensitive information, potentially corrupting databases or modifying application state without prior authentication. The lack of sufficient validation allows for persistent or transient data manipulation depending on the injected statement, posing a persistent threat to data integrity. The issue affects all instances of the postgres-mcp-server prior to version 1.1.7. This vulnerability underscores the necessity for comprehensive input filtering and the enforcement of the principle of least privilege at the database driver level, ensuring that even if a validation flaw exists, the underlying database connection lacks the necessary permissions to perform destructive or non-compliant operations."
}