CVE-2026-27699 is a critical-severity (CVSS 9.1) Path Traversal vulnerability in basic-ftp. A fix is available for basic-ftp — see the affected versions and patch details below.
Basic FTP has Path Traversal Vulnerability in its downloadToDir() method
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-27699.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
basic-ftpnpmDescription
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
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 filters exact . or .. entries
- No sanitization of ../ sequences in filenames
path.join()doesn't prevent traversal,fs.open()resolves paths
Impact
A malicious FTP server can: - Write files to arbitrary locations on the client filesystem - Overwrite critical system files (if user has write access) - Potentially achieve remote code execution
Affected Versions
- Tested: v5.1.0
- Likely: All versions (code pattern exists since initial implementation)
Mitigation
Workaround: Do not use downloadToDir() with untrusted FTP servers.
Fix: Sanitize filenames before use:
import { basename } from 'path'
// In _downloadFromWorkingDir:
const sanitizedName = basename(file.name) // Strip path components
const localPath = join(localDirPath, sanitizedName)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | basic-ftp | all versions | 5.2.0npm install basic-ftp@5.2.0 |
Affected Products
basic-ftppatrickjuchliDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for basic-ftp, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update basic-ftp to 5.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27699 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
In default configurations Red Hat on products affected applications do not allow for arbitrary file overwrites. The files which may be overwritten are scoped to the active user permissions that the process is executing with.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.Source: Red Hat security advisory for CVE-2026-27699 (CC BY 4.0)
Frequently Asked Questions
Is CVE-2026-27699 in your dependencies?
Find it across npm, including transitive dependencies.