CVE-2026-27699 — Basic FTP has Path Traversal Vulnerability in its downloadToDir() method

Affected: patrickjuchli basic-ftp

The `basic-ftp` FTP client library for Node.js contains a path traversal vulnerability (CWE-22) in versions prior to 5.2.0 in the `downloadToDir()` method. A malicious FTP server can send directory listings with filenames containing path traversal sequences (`../`) that cause files to be written outside the intended download directory. Version 5.2.0 patches the issue.

GHSA-5rq4-664w-9x2c — Basic FTP has Path Traversal Vulnerability in its downloadToDir() method

Affected: npm: basic-ftp

The `basic-ftp` library contains a path traversal vulnerability in the `downloadToDir()` method. A malicious FTP server can send directory listings with filenames containing path traversal sequences (`../`) that cause files to be written outside the intended download directory.

## Source-to-Sink Flow

``` 1. SOURCE: FTP server sends LIST response └─> "-rw-r--r-- 1 user group 1024 Jan 20 12:00 ../../../etc/passwd"

2. PARSER: parseListUnix.ts:100 extracts filename └─> file.name = "../../../etc/passwd"

3. VALIDATION: parseListUnix.ts:101 checks └─> if (name === "." || name === "..") ❌ (only filters exact matches) └─> "../../../etc/passwd" !== "." && !== ".." ✅ PASSES

4. SINK: Client.ts:707 uses filename directly └─> const localPath = join(localDirPath, file.name) └─> join("/safe/download", "../../../etc/passwd") └─> Result: "/safe/download/../../../etc/passwd" → resolves to "/etc/passwd"

5. FILE WRITE: Client.ts:512 opens file └─> fsOpen(localPath, "w") → writes to /etc/passwd (outside intended directory) ```

## Vulnerable Code

**File**: `src/Client.ts:707`

```typescript protected async _downloadFromWorkingDir(localDirPath: string): Promise<void> { await ensureLocalDirectory(localDirPath) for (const file of await this.list()) { const localPath = join(localDirPath, file.name) // ⚠️ VULNERABLE // file.name comes from untrusted FTP server, no sanitization await this.downloadTo(localPath, file.name) } } ```

**Root Cause**: - Parser validation (`parseListUnix.ts:101`) only…

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CVE-2026-27699 — Basic FTP has Path Traversal Vulnerability in its downloadToDir() method

GHSA-5rq4-664w-9x2c — Basic FTP has Path Traversal Vulnerability in its downloadToDir() method