A path traversal flaw in pnpm’s tarball extraction process allows malicious packages to write files outside the intended package directory on Windows. The path normalization logic only checks for the Unix‐style "." prefix, ignoring the backslash used on Windows; this oversight lets an attacker include file paths that escape the package boundary and overwrite critical files such as ".npmrc" or build configuration files, potentially leading to privilege escalation or arbitrary code execution.

pnpm users running on Windows and Windows‑based CI/CD environments, including GitHub Actions Windows runners and Azure DevOps pipelines, using version 10.28.0 or earlier. The vulnerability does not affect other operating systems.

The CVSS score of 6.5 reflects moderate severity, and the EPSS score of less than 1% suggests a low likelihood of exploitation at this time. The vulnerability is not listed in the CISA KEV catalogue. An attacker can exploit this flaw by introducing a malicious package into a locally built or CI‑driven project on a Windows machine, thereby gaining the ability to overwrite arbitrary files on the host.