CVE-2026-44240: basic-ftp allows a malicious FTP server to cause client-side denial of service via unbounded multiline control response buffering

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.