CVE-2025-47210: Qnap Qsync Central DOS Vulnerability

CVE-2025-47210 Overview

CVE-2025-47210 is a NULL pointer dereference vulnerability [CWE-476] affecting QNAP Qsync Central. An authenticated remote attacker with a valid user account can trigger the flaw to crash the service and cause a denial-of-service (DoS) condition. QNAP addressed the issue in Qsync Central version 5.0.0.2 released on 2025/07/31. The vulnerability requires low privileges and no user interaction, but its impact is limited to availability of the Qsync Central service.

Critical Impact
Authenticated remote attackers can trigger a NULL pointer dereference to disrupt QNAP Qsync Central file synchronization services, interrupting backup and collaboration workflows on affected NAS deployments.

Affected Products

QNAP Qsync Central versions prior to 5.0.0.2
QNAP NAS deployments running Qsync Central as a file synchronization service
Multi-user QNAP environments where remote accounts have access to Qsync Central

Discovery Timeline

2025-10-03 - CVE-2025-47210 published to the National Vulnerability Database (NVD)
2026-10-18 - Last updated in NVD database

Technical Details for CVE-2025-47210

Vulnerability Analysis

The vulnerability resides in QNAP Qsync Central, a centralized file synchronization application for QNAP NAS devices. A remote attacker who holds a valid user account can send crafted requests that cause the application to dereference a NULL pointer. The result is an application crash that interrupts synchronization services for all connected clients.

The flaw affects availability only. According to the QNAP advisory, confidentiality and integrity of stored data are not impacted. However, Qsync Central is often used to coordinate backups and file replication across teams, so service disruption can delay recovery and collaboration workflows.

Root Cause

The root cause is a missing NULL check [CWE-476] on a pointer referenced during request handling. When the pointer is uninitialized or has been freed, the subsequent dereference triggers a process fault. The QNAP advisory does not disclose the exact code path or input structure that reaches the vulnerable function.

Attack Vector

Exploitation requires network access to the Qsync Central service and an authenticated session with a low-privilege user account. The attacker sends a request that reaches the vulnerable code path, forcing the dereference. No user interaction is required on the victim side. The vulnerability cannot be triggered unauthenticated, which limits exposure to environments where attackers can obtain valid credentials through phishing, credential stuffing, or insider access.

QNAP has not published technical details or proof-of-concept code. See the QNAP Security Advisory QSA-25-35 for vendor guidance.

Detection Methods for CVE-2025-47210

Indicators of Compromise

Unexpected crashes or restarts of the Qsync Central service on QNAP NAS devices
Synchronization clients reporting repeated connection failures to the Qsync Central server
Authentication logs showing low-privilege accounts generating anomalous request volume prior to service failure

Detection Strategies

Monitor Qsync Central service logs for abnormal termination events and process restart patterns
Correlate authenticated API or synchronization requests with service availability drops to isolate triggering sessions
Alert on repeated service failures originating from the same authenticated user session or source IP address

Monitoring Recommendations

Forward QNAP system and application logs to a centralized log platform for correlation with authentication events
Track installed Qsync Central version across the NAS fleet to identify hosts running versions earlier than 5.0.0.2
Review account activity for Qsync Central users and flag accounts with repeated failed sessions or unusual geographic access

How to Mitigate CVE-2025-47210

Immediate Actions Required

Upgrade Qsync Central to version 5.0.0.2 (released 2025/07/31) or later on all affected QNAP NAS devices
Audit Qsync Central user accounts and remove or disable accounts that are inactive or no longer required
Enforce strong, unique passwords and enable two-factor authentication for all QNAP accounts with Qsync Central access

Patch Information

QNAP has fixed the vulnerability in Qsync Central 5.0.0.2 and later. Administrators should apply the update through the QNAP App Center on each affected device. Refer to the QNAP Security Advisory QSA-25-35 for the official release notes and download guidance.

Workarounds

Restrict network access to the Qsync Central service by placing the NAS behind a firewall or VPN until the patch is applied
Limit Qsync Central access to trusted internal IP ranges using the QNAP built-in access control lists
Temporarily disable the Qsync Central service on devices that cannot be updated immediately if synchronization is not business-critical

bash

# Example: restrict Qsync Central access using QNAP firewall rules
# Replace 10.0.0.0/24 with your trusted management subnet
iptables -A INPUT -p tcp --dport 8080 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP