CVE-2025-57155: OwnTone Server DoS Vulnerability

CVE-2025-57155 Overview

A NULL pointer dereference vulnerability has been identified in the daap_reply_groups function within src/httpd_daap.c in owntone-server through commit 5e6f19a (newer commit after version 28.2). This vulnerability allows remote attackers to cause a Denial of Service (DoS) condition by triggering a NULL pointer dereference in the affected function.

Critical Impact

Remote attackers can crash the OwnTone server without authentication, causing service disruption for media streaming users.

Affected Products

• OwnTone Server through commit 5e6f19a
• OwnTone Server versions after 28.2 (prior to the security fix)

Discovery Timeline

• 2026-01-20 - CVE-2025-57155 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2025-57155

Vulnerability Analysis

This vulnerability is classified as CWE-476 (NULL Pointer Dereference), a memory corruption flaw that occurs when the application attempts to use a pointer that has a NULL value. In the context of OwnTone Server, the daap_reply_groups function in the DAAP (Digital Audio Access Protocol) HTTP handler fails to properly validate pointer values before dereferencing them.

The DAAP protocol is used by OwnTone Server to share media libraries over a network. When processing group-related requests, the vulnerable function does not adequately check for NULL conditions, allowing a remote attacker to craft requests that trigger the NULL pointer dereference. This results in an immediate server crash, denying service to legitimate users.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and pointer checking within the daap_reply_groups function. The function processes incoming DAAP requests and builds response data structures, but fails to verify that all required data structures have been properly initialized before accessing them. When certain edge cases or malformed requests are processed, a pointer that should reference valid memory instead contains NULL, and the subsequent dereference causes the application to crash.

Attack Vector

The attack vector for CVE-2025-57155 is network-based, requiring no authentication or user interaction. An attacker can remotely send specially crafted HTTP requests to the DAAP endpoint of an exposed OwnTone Server. The vulnerability can be exploited over a network connection to the server's listening port (typically port 3689 for DAAP).

Since the attack requires no privileges and has low complexity, any attacker with network access to the server can trigger the crash. While the vulnerability does not allow data exfiltration or code execution, repeated exploitation can maintain a persistent denial of service condition.

The vulnerability manifests in the daap_reply_groups function when handling DAAP group enumeration requests. For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-57155

Indicators of Compromise

• Unexpected OwnTone Server process crashes or service restarts
• Core dump files generated by the owntone-server process indicating NULL pointer access
• Unusual HTTP request patterns targeting DAAP endpoints
• Log entries showing abnormal group enumeration requests to /databases/*/groups

Detection Strategies

• Monitor OwnTone Server process stability and implement alerting on unexpected restarts
• Analyze HTTP access logs for anomalous DAAP protocol requests
• Deploy network intrusion detection rules to identify malformed DAAP requests
• Implement application-level monitoring to detect crash patterns consistent with NULL pointer exceptions

Monitoring Recommendations

• Enable verbose logging in OwnTone Server to capture request details
• Configure system monitoring to alert on segmentation faults (SIGSEGV) from the owntone-server process
• Monitor network traffic for repeated connections followed by immediate disconnections on DAAP ports
• Set up automated service health checks to detect availability issues

How to Mitigate CVE-2025-57155

Immediate Actions Required

• Update OwnTone Server to a version containing commit d857116e4143a500d6a1ea13f4baa057ba3b0028 or later
• Restrict network access to the DAAP service using firewall rules to trusted clients only
• Consider temporarily disabling the DAAP service if not required
• Implement rate limiting on incoming connections to reduce DoS impact

Patch Information

A fix has been committed to the OwnTone Server repository. The security patch is available at GitHub commit d857116e. Users should update their installations to include this commit or wait for an official release that incorporates the fix.

For additional details, review the security advisory published by the security researchers.

Workarounds

• Restrict DAAP service access to trusted networks using firewall rules or network segmentation
• Deploy a reverse proxy with request validation to filter potentially malicious DAAP requests
• Implement connection rate limiting at the network level to mitigate DoS impact
• Temporarily disable the DAAP protocol if media sharing functionality is not critical

# Example: Restrict DAAP port access using iptables
# Allow DAAP connections only from trusted local 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