Bug 2490893 (CVE-2026-48774)

Summary: CVE-2026-48774 proxysql: ProxySQL: Unauthorized write operations via insufficient SQL statement validation.
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in ProxySQL, specifically within its GenAI/MCP (MySQL Proxy Control Plane) `run_sql_readonly` tool. This tool, designed for read-only operations, inadequately validates SQL statements. An attacker can exploit this by submitting a seemingly read-only initial SQL statement followed by a malicious, side-effecting statement. This bypasses the tool's security contract, allowing unauthorized write operations or the execution of administrative SQL commands on the backend database, limited by the configured account's privileges.
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Bug Depends On: 2491333, 2491332    
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Description OSIDB Bzimport 2026-06-19 20:01:04 UTC 
ProxySQL is a proxy for MySQL and its forks, as well as PostgreSQL. In versions 3.0.0 through 3.0.8, ProxySQL's GenAI/MCP `run_sql_readonly` tool violates its documented read-only contract for MySQL targets. The tool validates only the full input string with a substring blacklist and first-keyword allowlist, but then executes the entire SQL string on a backend connection created with `CLIENT_MULTI_STATEMENTS`. As a result, a caller can submit a read-only first statement followed by a side-effecting second statement, such as `SELECT 1; RENAME TABLE ...`. The validator accepts the payload because it starts with `SELECT` and because side-effecting MySQL statements such as `RENAME TABLE`, `SET`, `RESET`, `LOCK TABLES`, and `KILL` are not rejected by the blacklist. In a live MCP runtime test, the `/mcp/query` endpoint accepted a `run_sql_readonly` request. The MCP response reported success for the first `SELECT`, and direct backend verification showed that the table had actually been renamed. This violates the endpoint's read-only security contract and lets an MCP caller perform backend writes or administrative SQL, limited by the configured MCP target account's database privileges. Version 3.0.9 contains a fix. Other operator mitigations include: keeping MCP disabled unless required; setting a non-empty `mcp-query_endpoint_auth` token before exposing `/mcp/query`; restricting MCP listener network exposure; configuring MCP backend target credentials as database-level read-only users; and adding temporary MCP query rules to block obvious multi-statement patterns.