CVE-2025-63647: OwnTone Server DoS Vulnerability

CVE-2025-63647 Overview

A NULL pointer dereference vulnerability exists in the parse_meta function located in src/httpd_daap.c of owntone-server commit 334beb. This vulnerability allows remote attackers to cause a Denial of Service (DoS) condition by sending a specially crafted DAAP (Digital Audio Access Protocol) request to the server. When the malicious request is processed, the server attempts to dereference a NULL pointer, resulting in an application crash.

Critical Impact

Remote attackers can crash the owntone-server service without authentication, disrupting media streaming capabilities for all connected users and devices.

Affected Products

• owntone-server (commit 334beb and potentially earlier versions)
• Systems running owntone-server with DAAP protocol enabled
• Network-accessible owntone-server deployments

Discovery Timeline

• 2026-01-20 - CVE-2025-63647 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2025-63647

Vulnerability Analysis

This vulnerability is classified as CWE-476: NULL Pointer Dereference. The flaw resides in the parse_meta function within the DAAP HTTP handler (httpd_daap.c). When processing incoming DAAP requests, the function fails to properly validate certain input parameters before dereferencing them. This lack of input validation allows an attacker to craft a malicious DAAP request that triggers a NULL pointer dereference condition.

The DAAP protocol is used by owntone-server to share media libraries over a network, similar to iTunes sharing functionality. Because this service typically listens on network interfaces, the attack surface is accessible to any network-connected attacker who can reach the DAAP service port.

Root Cause

The root cause is insufficient input validation in the parse_meta function. The code assumes certain request parameters will always contain valid data and proceeds to dereference pointers without first checking if they are NULL. When an attacker sends a request with missing or malformed metadata fields, the parsing logic encounters a NULL pointer and attempts to dereference it, causing the application to crash.

This is a classic NULL pointer dereference pattern where defensive programming practices—specifically NULL checks before pointer operations—were not implemented for all code paths.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a target system running owntone-server with DAAP enabled
2. Crafting a malicious DAAP request with specific metadata fields omitted or malformed
3. Sending the request to the server's DAAP service port
4. The server processes the request, hits the NULL pointer dereference, and crashes

The vulnerability mechanism involves the improper handling of metadata parsing in DAAP requests. When the parse_meta function receives a request lacking expected metadata fields, it fails to validate pointer validity before dereferencing, leading to application termination. For technical implementation details, see the GitHub Security Advisory and the proof-of-concept repository.

Detection Methods for CVE-2025-63647

Indicators of Compromise

• Unexpected owntone-server process terminations or crashes
• Segmentation fault errors in system logs associated with owntone-server
• Unusual DAAP protocol traffic patterns, especially malformed requests
• Multiple service restart attempts in a short time period

Detection Strategies

• Monitor system logs for segmentation faults or NULL pointer dereference errors from the owntone-server process
• Implement network intrusion detection rules to identify malformed DAAP requests targeting the server
• Deploy application-level monitoring to detect abnormal crash patterns in the owntone-server service
• Analyze network traffic for unusual DAAP request structures that deviate from protocol specifications

Monitoring Recommendations

• Enable core dump collection for owntone-server to capture crash diagnostics
• Configure alerting on owntone-server service restarts to identify potential exploitation attempts
• Monitor DAAP service port traffic for anomalous connection patterns or request volumes
• Implement log aggregation to correlate crash events across multiple server instances

How to Mitigate CVE-2025-63647

Immediate Actions Required

• Update owntone-server to a patched version that includes the fix for commit 53ee9a3c3921e5448f502800c4dfa787865f6cb7
• Restrict network access to the DAAP service port to trusted networks or clients only
• Consider temporarily disabling DAAP functionality if not required for operations
• Implement network-level filtering to limit access to the owntone-server service

Patch Information

A fix has been committed to the owntone-server repository. The patch is available in commit 53ee9a3c3921e5448f502800c4dfa787865f6cb7. Users should update their owntone-server installation to a version that includes this commit or apply the patch manually if building from source.

Workarounds

• Restrict access to the DAAP service port using firewall rules to limit exposure to trusted networks only
• Deploy a reverse proxy or web application firewall in front of the DAAP service to filter malformed requests
• If DAAP functionality is not essential, disable the DAAP protocol in the owntone-server configuration
• Implement service monitoring with automatic restart capabilities to minimize downtime during potential attacks

# Example: Restrict DAAP port access using iptables
# Allow DAAP (typically port 3689) only from trusted network
iptables -A INPUT -p tcp --dport 3689 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 3689 -j DROP