In Netflix OSS Hollow, since the Files.exists(parent) is run before creating the directories, an attacker can pre-create these directories with wide permissions. Additionally, since an insecure source of randomness is used, the file names to be created can be deterministically calculated.

Affected: Maven: com.netflix.hollow:hollow

> ID: NFLX-2021-001 > Title: Local information disclosure in Hollow > Release Date: 2021-03-23 > Credit: Security Researcher @JLLeitschuh

# Overview

Security researcher @JLLeitschuh reported that Netflix Hollow (a Netflix OSS project available here: https://github.com/Netflix/hollow) writes to a local temporary directory before validating the permissions on it.

# Impact

An attacker with the ability to create directories and set permissions on the local filesystem could pre-create this directory and read or modify anything written there by the Hollow process.

# Description

Since the `Files.exists(parent)` is run before creating the directories, an attacker can pre-create these directories with wide permissions. Additionally, since an insecure source of randomness is used, the file names to be created can be deterministically calculated.

# Workarounds and Fixes

Avoid running Hollow in configurations that share a filesystem with less-trusted processes. May be fixed in a future release.