CVE-2026-55700: pnpm Path Traversal in Package Download

Technical summary

CVE-2026-55700 is a path traversal vulnerability in pnpm's `stage download` command. The vulnerable code derived a local filename from untrusted registry fields (package name and version) without proper validation, allowing directory traversal sequences in the manifest to escape the designated download directory. An attacker controlling a package manifest could cause arbitrary file overwrites on the system running pnpm. The vulnerability affects pnpm versions 11.3.0 through 11.5.2. The remediation implements input validation on both name and version fields, ensures a single safe filename is derived from the combined validated inputs, and performs path canonicalization to verify the final destination is within the intended download directory before file write operations.

Business impact

Organizations and developers using pnpm in automated deployment pipelines, CI/CD systems, or local development environments face risk of arbitrary file overwriting. An attacker could inject malicious packages into package registries (public or private) or conduct supply-chain attacks by compromising legitimate packages to include crafted manifests. This could lead to code injection, configuration tampering, or denial of service. Development teams relying on pnpm should prioritize remediation, particularly in unattended build systems where human review is minimal.

Affected systems

pnpm versions 11.3.0 through 11.5.2 are affected. The vulnerability is present in the package manager itself and impacts any system running a vulnerable version when downloading packages via the `pnpm stage download` command. This includes developer workstations, CI/CD runners, and container environments using affected pnpm versions. Users of pnpm 11.5.3 and later, as well as versions earlier than 11.3.0, are not affected.

Exploitability

The vulnerability requires user interaction in the form of running pnpm commands to download a crafted package. However, in CI/CD and automated build environments, this interaction is routine and unsupervised. An attacker must either compromise an existing package on a registry or inject a new malicious package, making exploitability dependent on registry access or supply-chain positioning. The attack has a network vector (registry-controlled manifest) and low attack complexity, though it does require a user to initiate the download action.

Remediation

Upgrade pnpm to version 11.5.3 or later immediately. This version includes the merged fix that validates both package name and version fields, derives a single safe filename from validated inputs, and verifies the final write destination is within the expected download directory. No configuration changes or workarounds are available for earlier versions; upgrading is the only mitigation.

Patch guidance

Update pnpm to 11.5.3 or later. For development teams: run `npm install -g pnpm@latest` or `pnpm self-update` if using a version within the affected range. For CI/CD systems: update lock files, container images, and build scripts that pin pnpm versions to 11.5.3 or later. Verify the upgrade by running `pnpm --version` and confirming output is 11.5.3 or higher. For teams unable to upgrade immediately, restrict pnpm usage to trusted internal packages only and avoid downloading from public registries.

Detection guidance

Monitor pnpm version usage across development and build infrastructure using `pnpm --version` checks in CI/CD logs and developer workstations. Review package download logs for unexpected file writes outside normal cache directories. Implement package manifest integrity checks by validating package names and versions against expected patterns before download. In CI/CD, capture and review the output of `pnpm stage download` commands for any warnings or errors related to path validation. Use filesystem auditing tools to detect unexpected file modifications in directories outside intended package cache locations.

Why prioritize this

This vulnerability scores HIGH (CVSS 7.1) due to its high integrity impact and low barriers to exploitation in automated environments. While it requires user interaction, that interaction is routine in build pipelines. The risk is elevated because pnpm is a critical dependency in the JavaScript ecosystem, and automated package downloads are common in CI/CD workflows where supply-chain attacks are increasingly frequent. Organizations should prioritize this within the next security update cycle.

Risk score, explained

CVSS 7.1 reflects a network-based attack vector, low attack complexity, no privilege requirements, and no confidentiality impact, but high integrity impact and low availability impact. The severity is driven by the ability to overwrite arbitrary files on affected systems, which could compromise code, configuration, or system stability. The user interaction requirement and single-user scope prevent a higher score, but the ease of exploitation in automated environments and the widespread use of pnpm justify the HIGH severity rating.

Frequently asked questions