CVE-2026-30976: Sonarr Information Disclosure Vulnerability

CVE-2026-30976 Overview

CVE-2026-30976 is a path traversal vulnerability affecting Sonarr, a popular PVR (Personal Video Recorder) application for Usenet and BitTorrent users. This vulnerability allows unauthenticated remote attackers to potentially read any file accessible by the Sonarr process on Windows systems. The impact is significant as attackers can access sensitive application configuration files containing API keys and database credentials, Windows system files, and any user-accessible files on the same drive.

Critical Impact

Unauthenticated attackers can remotely read sensitive files including API keys, database credentials, and system files on vulnerable Windows installations of Sonarr.

Affected Products

• Sonarr 4.x versions prior to 4.0.17.2950 (nightly/develop branch)
• Sonarr 4.x versions prior to 4.0.17.2952 (stable/main branch)
• Windows installations only (macOS and Linux are unaffected)

Discovery Timeline

• 2026-03-25 - CVE-2026-30976 published to NVD
• 2026-03-26 - Last updated in NVD database

Technical Details for CVE-2026-30976

Vulnerability Analysis

This vulnerability is classified as a path traversal flaw (CWE-22). The core issue lies in insufficient validation of file paths served through Sonarr's API endpoints. Files returned from the API were not properly restricted to their intended directory on disk, allowing attackers to traverse outside the expected directory structure.

The vulnerability enables unauthenticated remote attackers to exploit the API to read arbitrary files on the system. Since Sonarr runs as a service with specific permissions, any file readable by the Sonarr process becomes accessible to attackers. This includes sensitive configuration files that typically contain API keys and database credentials, potentially leading to further compromise of connected services.

The attack requires network access but does not require any privileges or user interaction, making it particularly dangerous for internet-exposed Sonarr instances. While the vulnerability is limited to information disclosure without direct integrity or availability impact, the exposure of credentials could enable subsequent attacks.

Root Cause

The root cause is improper input validation in the API file serving functionality. The application failed to properly sanitize and validate file path requests, allowing directory traversal sequences (such as ../) to escape the intended directory boundaries. This is a classic path traversal weakness where user-controlled input is used to construct file paths without adequate validation.

Attack Vector

An attacker can exploit this vulnerability remotely over the network without authentication. The attack targets the API endpoints responsible for serving files. By crafting malicious requests containing path traversal sequences, an attacker can navigate outside the intended directory structure and access arbitrary files readable by the Sonarr process.

The exploitation is straightforward—attackers send specially crafted HTTP requests to the Sonarr API with manipulated file path parameters. The server processes these requests without properly validating that the requested file resides within the expected directory, returning the contents of the targeted file to the attacker.

On Windows systems, this could allow access to:

• Sonarr configuration files containing API keys and credentials
• Windows system files such as win.ini or registry hives
• Any user files accessible to the account running Sonarr

Detection Methods for CVE-2026-30976

Indicators of Compromise

• Unusual API requests containing path traversal patterns such as ../, ..\\, or URL-encoded variants
• Access logs showing requests for files outside Sonarr's normal operational directories
• Unexpected access to configuration files like config.xml from external IP addresses
• Failed or successful reads of Windows system files through Sonarr's API endpoints

Detection Strategies

• Monitor Sonarr API access logs for path traversal patterns including ../, ..%2F, and similar encoded sequences
• Implement web application firewall (WAF) rules to detect and block directory traversal attempts
• Review authentication logs for API access from unexpected or unauthorized sources
• Set up alerts for any access to sensitive system paths through the Sonarr application

Monitoring Recommendations

• Enable detailed logging for Sonarr API requests and regularly audit for anomalous patterns
• Monitor network traffic for suspicious file read operations targeting configuration or system files
• Implement file integrity monitoring on sensitive configuration files to detect unauthorized access
• Review Sonarr version across deployments to identify unpatched instances

How to Mitigate CVE-2026-30976

Immediate Actions Required

• Update Sonarr to version 4.0.17.2950 or later (nightly/develop branch) or 4.0.17.2952 or later (stable/main branch)
• Restrict network access to Sonarr instances, ensuring they are not directly exposed to the internet
• Review API keys and credentials stored in Sonarr configuration files; rotate them if exposure is suspected
• Audit access logs for any signs of exploitation prior to patching

Patch Information

The Sonarr development team has released patches addressing this vulnerability. Users should update to the following versions:

• Nightly/Develop Branch: Version 4.0.17.2950
• Stable/Main Branch: Version 4.0.17.2952

For complete details, refer to the GitHub Security Advisory GHSA-h393-v5hm-6h8f.

Workarounds

• Host Sonarr only on a secure internal network isolated from direct internet access
• Access Sonarr remotely via VPN, Tailscale, or similar secure tunneling solutions
• Implement reverse proxy with authentication in front of Sonarr instances
• Configure firewall rules to restrict access to Sonarr's listening ports to trusted IP addresses only

# Example: Restrict Sonarr access using Windows Firewall
# Block external access to Sonarr port (default 8989)
netsh advfirewall firewall add rule name="Block Sonarr External" dir=in action=block protocol=tcp localport=8989 profile=public

# Allow access only from trusted internal network
netsh advfirewall firewall add rule name="Allow Sonarr Internal" dir=in action=allow protocol=tcp localport=8989 remoteip=192.168.1.0/24 profile=private