In this post, we will discuss a critical vulnerability (CVE-2023-2454) found in the popular open-source database management system, PostgreSQL. This vulnerability allows an authenticated attacker with elevated database-level privileges to execute arbitrary code by defeating the protective search_path changes. This vulnerability has significant security implications and could potentially lead to unauthorized access to sensitive information and even complete control of a vulnerable PostgreSQL server. We will delve into the details of this vulnerability, including code snippets, links to original references, and exploit details.

Background

PostgreSQL is a powerful, enterprise-class open-source database management system that emphasizes extensibility, data integrity, and SQL compliance. It is used by countless businesses and organizations worldwide as the backbone of their data-driven applications.

CVE-2023-2454 refers to a specific vulnerability discovered in PostgreSQL, where Schema_Element (part of a SQL statement) can bypass or defeat the protective search_path changes implemented by the security team. The search_path is a run-time parameter in PostgreSQL, which determines the schema search order when querying objects in the database.

Vulnerability Details

The vulnerability resides in the way PostgreSQL handles certain database calls, especially when a user-defined schema exists alongside the public schema. An attacker with elevated privileges can manipulate the search_path to include a user-defined schema, forcing subsequent SQL queries to resolve the objects in their schema instead of the intended public schema before executing arbitrary code.

Here is a code snippet that demonstrates the issue

-- Attacker creates a malicious function.
CREATE SCHEMA attacker_schema;
CREATE FUNCTION attacker_schema.attacker_function() RETURNS VOID AS $$...$$ LANGUAGE plpgsql;

-- Attacker changes the search_path to include the malicious attacker_schema.
SET search_path TO attacker_schema, public;

-- Victim unwittingly calls the malicious attacker_function through a vulnerable function.
SELECT public.vulnerable_function();

As seen in the code snippet above, the attacker is able to create a malicious function within their schema (attacker_schema) and alter the search_path to prioritize their schema over the public schema. This causes the subsequent call to the public function vulnerable_function to resolve to the attacker_function instead, executing the arbitrary code in the attacker_function.

The attacker must be authenticated with elevated database-level privileges.

2. The attacker must have the ability to create a user-defined schema and define functions within that schema.
3. The attacker must be able to manipulate the search_path or make use of existing functions with a vulnerable search_path.

Once these conditions are met, the attacker can use the code snippet above to manipulate the search_path, create a malicious function, and execute arbitrary code through existing public functions.

1. Official PostgreSQL Security Announcement
2. CVE-2023-2454 - NVD
3. MITRE - CVE-2023-2454

Mitigation

In order to mitigate this vulnerability, PostgreSQL security team has released patches for the affected versions. Users are advised to update their PostgreSQL installations to the latest version and revisit their database functions and schemas to address any vulnerabilities resulting from the search_path manipulation by authenticated users with elevated privileges.

Conclusion

CVE-2023-2454 exposes a critical vulnerability in PostgreSQL, where unauthorized code execution can occur due to Schema_Element defeating the protective search_path changes. It is crucial that administrators of PostgreSQL installations follow best practices for securing their systems, including regular security patching and careful management of access privileges. Stay informed about security vulnerabilities like this one and take appropriate measures to protect your systems and data.

Timeline

Published on: 06/09/2023 19:15:00 UTC
Last modified on: 06/16/2023 18:00:00 UTC