CVE-2025-30266 Overview
CVE-2025-30266 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 cause a denial-of-service (DoS) condition against the Qsync Central service. The issue is tracked under QNAP advisory QSA-26-02 and is resolved in Qsync Central 5.0.0.4 and later.
Critical Impact
An authenticated remote attacker can disrupt Qsync Central availability, preventing legitimate file synchronization across QNAP NAS environments.
Affected Products
- QNAP Qsync Central (versions prior to 5.0.0.4)
- QNAP NAS deployments running vulnerable Qsync Central builds
- Environments using Qsync Central for centralized file synchronization
Discovery Timeline
- 2026-02-11 - CVE-2025-30266 published to NVD
- 2026-02-11 - Last updated in NVD database
Technical Details for CVE-2025-30266
Vulnerability Analysis
The vulnerability is a NULL pointer dereference within QNAP Qsync Central, classified under [CWE-476]. A remote attacker who has obtained a user account can send crafted input that causes the application to dereference a NULL pointer. The resulting fault crashes the affected process and disrupts service availability.
The CVSS 4.0 vector indicates a network attack vector requiring low privileges and passive attack requirements, with impact limited to availability of the vulnerable system. There is no confidentiality or integrity impact, and the scope does not cross into subsequent systems. The EPSS probability is 0.05%, reflecting low observed exploitation likelihood at this time.
Root Cause
The root cause is missing validation of a pointer prior to dereference within Qsync Central request handling logic. When the affected code path receives specific input from an authenticated session, it accesses memory through a pointer that has not been initialized or returned NULL from an earlier allocation or lookup. The dereference triggers a segmentation fault that terminates the service.
Attack Vector
Exploitation requires network access to Qsync Central and valid user credentials. An attacker submits crafted requests through an authenticated session to reach the vulnerable code path. The service crashes, producing a denial-of-service condition. No code execution, privilege escalation, or data disclosure results from successful exploitation. See the QNAP Security Advisory QSA-26-02 for vendor-confirmed technical details.
Detection Methods for CVE-2025-30266
Indicators of Compromise
- Repeated unexpected termination or restart of the Qsync Central service process on QNAP NAS devices.
- Authentication followed by anomalous request patterns from a single user account targeting Qsync Central endpoints.
- Service availability alerts and synchronization failures reported by Qsync Central clients.
Detection Strategies
- Monitor Qsync Central process status and crash logs on QNAP NAS systems for repeated abnormal exits.
- Correlate authenticated session activity with service crashes to identify abuse patterns tied to specific user accounts.
- Review QNAP system logs for stack traces or fault entries referencing Qsync Central modules.
Monitoring Recommendations
- Enable centralized logging from QNAP NAS appliances and forward events to a SIEM for correlation.
- Alert on Qsync Central service restarts that exceed a defined baseline frequency.
- Track failed and successful authentication events against Qsync Central to identify low-privilege accounts attempting unusual operations.
How to Mitigate CVE-2025-30266
Immediate Actions Required
- Upgrade Qsync Central to version 5.0.0.4 or later as released by QNAP.
- Audit Qsync Central user accounts and remove inactive or unnecessary credentials to reduce the authenticated attack surface.
- Restrict network exposure of Qsync Central to trusted management segments only.
Patch Information
QNAP has addressed CVE-2025-30266 in Qsync Central 5.0.0.4 and later. Administrators should apply the update through the QNAP App Center on each affected NAS. Refer to the QNAP Security Advisory QSA-26-02 for official remediation guidance.
Workarounds
- Limit Qsync Central access using firewall rules to restrict reachability to trusted internal subnets.
- Enforce strong password policies and multi-factor authentication on all QNAP user accounts.
- Disable the Qsync Central service on NAS devices where centralized synchronization is not required until patching is complete.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
