Sonarr Authentication Bypass Vulnerability Allowing Unauthorized Access

A vulnerability in Sonarr versions prior to 4.0.16.2942 allows authentication bypass for users who disabled authentication for local addresses. This issue arises when Sonarr is not behind a properly configured reverse proxy that handles the X-Forwarded-For header, leaving the application exposed to unauthorized access.

Impact

Exploitation of this vulnerability allows for authentication bypass, potentially leading to unauthorized access to the application.

Remediation

Users can upgrade to Sonarr version 4.0.16.2942 in the nightly/develop branch or version 4.0.16.2944 for stable/main releases. Additionally, ensure that Sonarr's Authentication Required setting is enabled, run Sonarr behind a reverse proxy configured for X-Forwarded-For header handling, and avoid exposing Sonarr directly to the internet. Instead, access it through a VPN, Tailscale, or a similar solution.