CVE-2025-52855 Overview
CVE-2025-52855 is a NULL pointer dereference vulnerability affecting multiple versions of QNAP QTS and QuTS hero operating systems. An authenticated remote attacker holding an administrator account can trigger the flaw to cause a denial-of-service (DoS) condition on the affected NAS device. The issue is tracked under CWE-476 and disclosed in QNAP Security Advisory QSA-25-36. QNAP resolved the vulnerability in QTS 5.2.6.3195 build 20250715 and QuTS hero h5.2.6.3195 build 20250715.
Critical Impact
An authenticated administrator can crash the affected QNAP OS service, disrupting NAS availability and any dependent storage or backup workflows.
Affected Products
- QNAP QTS versions prior to 5.2.6.3195 build 20250715
- QNAP QuTS hero versions prior to h5.2.6.3195 build 20250715
- QNAP NAS appliances running the affected QTS and QuTS hero builds listed in QSA-25-36
Discovery Timeline
- 2025-10-03 - CVE-2025-52855 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-52855
Vulnerability Analysis
The flaw is a NULL pointer dereference in a component of QNAP QTS and QuTS hero. When the vulnerable code path executes, it dereferences a pointer that was not initialized or was set to NULL. The resulting memory access fault terminates the affected process. On a NAS platform, this translates directly into a denial-of-service condition against the management or storage services provided by the operating system.
Exploitation requires an authenticated session with administrator privileges. That precondition limits mass exploitation but does not eliminate risk. Attackers who obtain administrator credentials through phishing, credential stuffing, or reuse from prior breaches can weaponize the flaw to disrupt storage availability. Insider threats with legitimate administrative access can also trigger the fault.
The EPSS score is 0.356%, indicating low observed exploitation likelihood in the wild at the time of writing. No public proof-of-concept and no CISA KEV listing exist for this CVE.
Root Cause
The root cause is missing validation of a pointer prior to dereference in an administrative code path of the QNAP operating system. QNAP has not published low-level code details in the public advisory. The CWE-476 classification confirms the fault pattern: control flow reaches an instruction that reads or writes through a pointer whose value is NULL.
Attack Vector
The attack vector is network-based. A remote attacker authenticated as an administrator sends a crafted request to the vulnerable service. The service processes the request, hits the unchecked pointer, and crashes. No user interaction is required, and no additional privileges beyond administrator are needed. Successful exploitation impacts availability only. Confidentiality and integrity are not affected according to the CVSS 4.0 vector.
No verified proof-of-concept code is publicly available. See the QNAP Security Advisory QSA-25-36 for vendor-provided technical context.
Detection Methods for CVE-2025-52855
Indicators of Compromise
- Unexpected termination or restart of QNAP system services on affected QTS or QuTS hero builds
- Administrator login events from unfamiliar source addresses immediately preceding a service crash
- Repeated 5xx responses or connection resets from the QNAP management interface
- Kernel or process crash entries referencing NULL pointer or segmentation faults in QNAP system logs
Detection Strategies
- Correlate administrator authentication events with subsequent NAS service crashes or reboots to identify possible triggering activity.
- Monitor QNAP System Event Logs and System Connection Logs for administrator sessions from unexpected geolocations or IP ranges.
- Alert on repeated abnormal restarts of QNAP services within short time windows, which may indicate exploitation attempts.
Monitoring Recommendations
- Forward QNAP syslog output to a centralized log platform for retention and correlation with identity events.
- Enable and review QNAP notification rules for service failures, disk unmounts, and administrator logins.
- Track administrator account usage patterns and flag deviations from established baselines.
How to Mitigate CVE-2025-52855
Immediate Actions Required
- Upgrade QTS to 5.2.6.3195 build 20250715 or later, and QuTS hero to h5.2.6.3195 build 20250715 or later.
- Restrict administrative access to the QNAP web interface to trusted management networks only.
- Enforce strong, unique passwords and multi-factor authentication for all administrator accounts.
- Audit administrator accounts and remove any that are unused, shared, or unnecessary.
Patch Information
QNAP has released fixed builds for both affected operating systems. Apply the patches described in QNAP Security Advisory QSA-25-36. Fixed versions are QTS 5.2.6.3195 build 20250715 and QuTS hero h5.2.6.3195 build 20250715. Use the QNAP Control Panel → System → Firmware Update workflow to install the update, or download the firmware image directly from the QNAP support portal.
Workarounds
- Disable remote access to the administrative interface, exposing management only through a VPN or bastion host until patching is complete.
- Limit inbound access to the QNAP web UI using the built-in firewall or an upstream network ACL.
- Reduce the number of accounts with administrator privileges and use least-privilege roles for routine operations.
# Example: restrict QNAP admin interface access at the network edge
# Allow only the management subnet to reach the QNAP HTTPS console
iptables -A INPUT -p tcp -s 10.10.20.0/24 --dport 443 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
