CVE-2026-27699: Basic ftp Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-5rq4-664w-9x2c",
  "modified" : "2026-02-25T22:34:26Z",
  "published" : "2026-02-25T22:34:26Z",
  "aliases" : [ "CVE-2026-27699" ],
  "summary" : "Basic FTP has Path Traversal Vulnerability in its downloadToDir() method",
  "details" : "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.\n\n\n## Source-to-Sink Flow\n\n```\n1. SOURCE: FTP server sends LIST response\n└─> \"-rw-r--r-- 1 user group 1024 Jan 20 12:00 ../../../etc/passwd\"\n\n2. PARSER: parseListUnix.ts:100 extracts filename\n└─> file.name = \"../../../etc/passwd\"\n\n3. VALIDATION: parseListUnix.ts:101 checks\n└─> if (name === \".\" || name === \"..\") ❌ (only filters exact matches)\n└─> \"../../../etc/passwd\" !== \".\" && !== \"..\" ✅ PASSES\n\n4. SINK: Client.ts:707 uses filename directly\n└─> const localPath = join(localDirPath, file.name)\n└─> join(\"/safe/download\", \"../../../etc/passwd\")\n└─> Result: \"/safe/download/../../../etc/passwd\" → resolves to \"/etc/passwd\"\n\n5. FILE WRITE: Client.ts:512 opens file\n└─> fsOpen(localPath, \"w\") → writes to /etc/passwd (outside intended directory)\n```\n\n## Vulnerable Code\n\n**File**: `src/Client.ts:707`\n\n```typescript\nprotected async _downloadFromWorkingDir(localDirPath: string): Promise<void> {\nawait ensureLocalDirectory(localDirPath)\nfor (const file of await this.list()) {\nconst localPath = join(localDirPath, file.name) // ⚠️ VULNERABLE\n// file.name comes from untrusted FTP server, no sanitization\nawait this.downloadTo(localPath, file.name)\n}\n}\n```\n\n**Root Cause**:\n- Parser validation (`parseListUnix.ts:101`) only filters exact `.` or `..` entries\n- No sanitization of `../` sequences in filenames\n- `path.join()` doesn't prevent traversal, `fs.open()` resolves paths\n\n\n# Impact\n\nA malicious FTP server can:\n- Write files to arbitrary locations on the client filesystem\n- Overwrite critical system files (if user has write access)\n- Potentially achieve remote code execution\n\n## Affected Versions\n\n- **Tested**: v5.1.0\n- **Likely**: All versions (code pattern exists since initial implementation)\n\n## Mitigation\n\n**Workaround**: Do not use `downloadToDir()` with untrusted FTP servers.\n\n**Fix**: Sanitize filenames before use:\n\n```typescript\nimport { basename } from 'path'\n\n// In _downloadFromWorkingDir:\nconst sanitizedName = basename(file.name) // Strip path components\nconst localPath = join(localDirPath, sanitizedName)\n```",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "basic-ftp"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "5.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/patrickjuchli/basic-ftp/security/advisories/GHSA-5rq4-664w-9x2c"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27699"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/patrickjuchli/basic-ftp/commit/2a2a0e6514357b9eda07c2f8afbd3f04727a7cd9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/patrickjuchli/basic-ftp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/patrickjuchli/basic-ftp/releases/tag/v5.2.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-25T22:34:26Z",
    "nvd_published_at" : "2026-02-25T15:20:53Z"
  }
}