CVE-2026-27699
ADVISORY - githubSummary
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)
Common Weakness Enumeration (CWE)
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
GitHub
3.9
CVSS SCORE
9.1critical| Package | Type | OS Name | OS Version | Affected Ranges | Fix Versions |
|---|---|---|---|---|---|
| basic-ftp | npm | - | - | <5.2.0 | 5.2.0 |
CVSS:3 Severity and metrics
The CVSS metrics represent different qualitative aspects of a vulnerability that impact the overall score, as defined by the CVSS Specification.
The vulnerable component is bound to the network stack, but the attack is limited at the protocol level to a logically adjacent topology. This can mean an attack must be launched from the same shared physical (e.g., Bluetooth or IEEE 802.11) or logical (e.g., local IP subnet) network, or from within a secure or otherwise limited administrative domain (e.g., MPLS, secure VPN to an administrative network zone). One example of an Adjacent attack would be an ARP (IPv4) or neighbor discovery (IPv6) flood leading to a denial of service on the local LAN segment (e.g., CVE-2013-6014).
Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.
The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
The vulnerable system can be exploited without interaction from any user.
An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
There is no loss of confidentiality.
There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any or all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component.
NIST
3.9
CVSS SCORE
9.1criticalRed Hat
3.9