CVE-2025-53407: QNAP QTS Format String Vulnerability

CVE-2025-53407 Overview

CVE-2025-53407 is an externally-controlled format string vulnerability [CWE-134] affecting multiple versions of QNAP QTS and QuTS hero operating systems. An authenticated remote attacker with administrator privileges can exploit the flaw to disclose sensitive memory contents or modify memory on the affected NAS device. QNAP addressed the issue in QTS 5.2.6.3195 build 20250715 and QuTS hero h5.2.6.3195 build 20250715. The vendor published details in QNAP Security Advisory QSA-25-36.

Critical Impact
A remote attacker holding administrator credentials can read secret data or corrupt process memory on affected QNAP appliances, undermining confidentiality and integrity of the NAS.

Affected Products

QNAP QTS 5.2.x (versions prior to 5.2.6.3195 build 20250715)
QNAP QuTS hero h5.2.x (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-2025-53407 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-53407

Vulnerability Analysis

The vulnerability stems from a use of externally-controlled format string weakness within components of QNAP QTS and QuTS hero. When user-supplied input reaches a formatted output function without a fixed format specifier, the input itself is parsed for format tokens such as %s, %x, or %n. This behavior allows the caller to read arbitrary values from the process stack or write to attacker-chosen memory addresses. Exploitation requires an authenticated administrator session, which limits the pool of viable attackers but does not eliminate risk from stolen credentials, insider threats, or lateral movement following an initial compromise.

Root Cause

The root cause is the direct use of externally-controlled data as a format argument in a variadic formatting routine. Secure coding practice requires a fixed format string with the untrusted value passed as a separate argument, such as printf("%s", user_input) rather than printf(user_input). QNAP's fix in the 5.2.6.3195 build 20250715 series enforces this pattern in the affected code paths.

Attack Vector

Exploitation occurs over the network against the QTS or QuTS hero management interface. The attacker must first authenticate with administrator privileges, then submit crafted input containing format specifiers to the vulnerable endpoint. Successful exploitation yields memory disclosure of secrets residing in the target process, or memory corruption that can alter program state. No user interaction is required beyond attacker-supplied input.

See the QNAP Security Advisory QSA-25-36 for the vendor's technical description.

Detection Methods for CVE-2025-53407

Indicators of Compromise

Administrator-authenticated HTTP requests to QTS or QuTS hero management endpoints containing format specifier sequences such as %s, %x, %p, or %n in parameter values.
Unexpected crashes, segmentation faults, or restarts of QTS or QuTS hero backend services logged in system diagnostics.
Anomalous administrator logins from unfamiliar IP addresses preceding malformed API requests.

Detection Strategies

Enable and centralize QNAP system, connection, and event logs, then alert on administrator sessions issuing requests with embedded format tokens.
Correlate administrator authentication events with immediate service errors or process restarts to surface exploitation attempts.
Review firmware and build versions across the fleet to identify appliances still running affected QTS or QuTS hero releases.

Monitoring Recommendations

Forward NAS syslog and audit events to a centralized SIEM or data lake for retention and pattern analysis.
Monitor administrator account activity for logins from new geolocations, off-hours access, and rapid configuration changes.
Track exposure of the QNAP web management interface to untrusted networks and alert on any external administrator authentication.

How to Mitigate CVE-2025-53407

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, as directed in QSA-25-36.
Rotate administrator credentials and enforce multi-factor authentication on all administrative accounts.
Audit the administrator account list and remove unused or shared accounts to reduce the attacker pool.

Patch Information

QNAP fixed the vulnerability in QTS 5.2.6.3195 build 20250715 and QuTS hero h5.2.6.3195 build 20250715. Apply the updates through the QTS Control Panel under System > Firmware Update, or download the firmware directly from the QNAP support portal. Details are documented in QNAP Security Advisory QSA-25-36.

Workarounds

Restrict access to the QNAP management interface to trusted management networks or VPN clients until the firmware update is applied.
Disable remote administrator access over the internet and block inbound access to management ports at the network perimeter.
Limit the number of accounts holding administrator privileges and monitor those accounts closely for anomalous behavior.

bash

# Verify installed QTS or QuTS hero build via SSH
getcfg System Version
getcfg System "Build Number"

# Expected minimum fixed versions:
#   QTS:        5.2.6.3195 build 20250715
#   QuTS hero:  h5.2.6.3195 build 20250715