GHSA-rp42-5vxx-qpwr

Summary

basic-ftp@5.2.2 is vulnerable to denial of service through unbounded memory growth while processing directory listings from a remote FTP server. A malicious or compromised server can send an extremely large or never-ending listing response to Client.list(), causing the client process to consume memory until it becomes unstable or crashes.

Details

The issue is in the package's default directory listing flow.

Client.list() reaches dist/Client.js, where the full listing response is downloaded into a StringWriter before parsing:

File: dist/Client.js:516-527

async _requestListWithCommand(command) {
    const buffer = new StringWriter_1.StringWriter();
    await (0, transfer_1.downloadTo)(buffer, {
        ftp: this.ftp,
        tracker: this._progressTracker,
        command,
        remotePath: "",
        type: "list"
    });
    const text = buffer.getText(this.ftp.encoding);
    this.ftp.log(text);
    return this.parseList(text);
}

The vulnerable sink is StringWriter, which grows an in-memory Buffer with no limit:

File: dist/StringWriter.js:5-20

class StringWriter extends stream_1.Writable {
    constructor() {
        super(...arguments);
        this.buf = Buffer.alloc(0);
    }
    _write(chunk, _, callback) {
        if (chunk instanceof Buffer) {
            this.buf = Buffer.concat([this.buf, chunk]);
            callback(null);
        }
        else {
            callback(new Error("StringWriter expects chunks of type 'Buffer'."));
        }
    }
    getText(encoding) {
        return this.buf.toString(encoding);
    }
}

The critical operation is:

this.buf = Buffer.concat([this.buf, chunk]);

There is no maximum size check, no truncation, and no streaming parser. Because the remote FTP server controls the listing response, it can force the client to keep allocating memory until the process is terminated.

How it happens:

1. An application connects to an attacker-controlled or...