Affected: npm: basic-ftp

## Summary

`basic-ftp` is vulnerable to client-side denial of service when parsing FTP control-channel multiline responses.

A malicious or compromised FTP server can send an unterminated multiline response during the initial FTP banner phase, before authentication. The client keeps appending attacker-controlled data into `FtpContext._partialResponse` and repeatedly reparses the accumulated buffer without enforcing a maximum control response size.

As a result, an application using `basic-ftp` can remain stuck in `connect()` while memory and CPU usage grow under attacker-controlled input. This can lead to process-level denial of service, container OOM kills, worker restarts, queue backlog, or service degradation in applications that automatically connect to FTP endpoints.

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## Details

### Root cause

The root cause is that incomplete FTP multiline control responses are buffered without an upper bound.

`FtpContext` stores incomplete control-channel data in `_partialResponse`:

https://github.com/patrickjuchli/basic-ftp/blob/50827c73ca6c1d786c97276e47be8a33d0f2277d/src/FtpContext.ts#L63-L64

Incoming control-channel data is handled in `_onControlSocketData`. The implementation concatenates the previous incomplete response with the new chunk, parses the entire accumulated string, and stores `parsed.rest` back into `_partialResponse`:

https://github.com/patrickjuchli/basic-ftp/blob/50827c73ca6c1d786c97276e47be8a33d0f2277d/src/FtpContext.ts#L328-L340

The relevant flo…