Zip Slip Path Traversal in coder/code-marketplace

Summary

A Zip Slip (CWE-22) vulnerability in coder/code-marketplace ≤ v2.4.1 allowed a malicious VSIX file to write arbitrary files outside the extension directory. ExtractZip passed raw zip entry names to a callback that wrote files via filepath.Join with no boundary check; filepath.Join resolved .. components but did not prevent the result from escaping the base path.

Root Cause

ExtractZip passed the raw, attacker-controlled zf.Name to a caller-supplied callback:

return false, fn(zf.Name, zr)  // zf.Name not sanitized

AddExtension constructed the output path with filepath.Join and no boundary check:

path := filepath.Join(dir, name)              // zip loop
path := filepath.Join(dir, file.RelativePath) // extra files loop

filepath.Clean resolved .. lexically but did not confine the result to dir:

filepath.Join("/srv/ext/pub/1.0", "../../../../etc/cron.d/evil")
  → "/etc/cron.d/evil"

Attack Scenario

An authenticated user (any upload-capable role) would submit a VSIX containing path-traversal entries.

On extraction, files would land at attacker-chosen paths writable by the marketplace process, enabling persistence (cron/init injection), SSH key injection, ld.so.preload hijacking, or binary overwrite depending on process privileges.

Fix

Addressed in https://github.com/coder/code-marketplace/releases/tag/v2.4.2

Recognition

Coder would like to thank Kandlaguduru Vamsi for responsibly disclosing this issue in accordance with https://coder.com/security/policy