VulnerabilityPublished 2 Jan 2026Updated 5 Jan 2026

CVE-2025-53591: QNAP Systems QTS · CWE-134

Affects QNAP Systems QTSSource CVE Database V5

Not known to be exploited · CVSS 1.2 Low : upgrade to 5.2.7.3256 build 20250913 when convenient.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 4.0 base score

1.2Low

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 27% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.2.7.3256 build 20250913, h5.3.1.3250 build 20250912, h5.2.7.3256 build 20250913

CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: High
User Interaction: None
Vulnerable system confidentiality: None
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: Unreported

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: High: The attacker requires privileges that provide significant (e.g., administrative) control over the vulnerable system allowing full access to the vulnerable system’s settings and files.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: Unreported: Based on threat intelligence sources each of the following must apply: · No knowledge of publicly available proof-of-concept · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 2 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade QTS to 5.2.7.3256 build 20250913; QuTS hero to h5.3.1.3250 build 20250912 or h5.2.7.3256 build 20250913.

Affected software

Product	Affected	Fixed in
QNAP Systems Inc.QTS	Affected =>=5.2.0 <5.3.0	Fixed in 5.2.7.3256 build 20250913
QNAP Systems Inc.QuTS hero	Affected ≥ h5.3.x, < h5.3.1.3250 build 20250912 ≥ h5.2.x, < h5.2.7.3256 build 20250913	Fixed in h5.3.1.3250 build 20250912 h5.2.7.3256 build 20250913

AI-suggested

European organizations should immediately verify the QTS or QuTS hero versions running on their QNAP NAS devices and upgrade to the fixed versions: QTS 5.2.7.3256 build 20250913 or later, and QuTS hero h5.2.7.3256 build 20250913 or later. Network segmentation should be enforced to limit administrative access to NAS devices only to trusted internal hosts and administrators. Strong authentication mechanisms, including multi-factor authentication for administrator accounts, should be implemented to reduce the risk of credential compromise. Regular audits of administrator account activity and logs can help detect suspicious behavior indicative of exploitation attempts. Additionally, organizations should ensure that firmware and software updates are applied promptly as part of their patch management process. Disabling unnecessary services and restricting remote administrative access via VPN or secure channels can further reduce exposure. Finally, organizations should maintain offline backups to recover from potential data corruption or loss.

Description

A use of externally-controlled format string vulnerability has been reported to affect several QNAP operating system versions. If a remote attacker gains an administrator account, they can then exploit the vulnerability to obtain secret data or modify memory. We have already fixed the vulnerability in the following versions: QTS 5.2.7.3256 build 20250913 and later QuTS hero h5.2.7.3256 build 20250913 and later QuTS hero h5.3.1.3250 build 20250912 and later

Impact

For European organizations, the impact of CVE-2025-53591 is primarily tied to the confidentiality and integrity of data stored on QNAP NAS devices. If exploited, an attacker with admin access could extract sensitive information or manipulate system memory, potentially leading to data breaches or system instability. Given that NAS devices often store critical business data and backups, unauthorized access or data corruption could disrupt operations and lead to compliance violations under regulations such as GDPR. However, the requirement for administrative privileges significantly reduces the risk of remote exploitation by external attackers without prior access. The low CVSS score indicates limited direct impact, but the vulnerability could be leveraged as part of a multi-stage attack within compromised networks. European organizations relying heavily on QNAP NAS for storage, especially in sectors like finance, healthcare, and government, should consider this vulnerability a moderate risk until patched.

CWE-134Use of Externally-Controlled Format String (opens in a new tab)
Base weaknessLikelihood of exploit: High
The product uses a function that accepts a format string as an argument, but the format string originates from an external source.
Requirements
Choose a language that is not subject to this flaw.
Implementation
Ensure that all format string functions are passed a static string which cannot be controlled by the user, and that the proper number of arguments are always sent to that function as well. If at all possible, use functions that do not support the %n operator in format strings.
Build and Compilation
Run compilers and linkers with high warning levels, since they may detect incorrect usage.
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V5.4.2 (opens in a new tab)
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
Attack patterns
Format String Injection (opens in a new tab)
String Format Overflow in syslog() (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

qnap.com/en/security-advisory/qsa-25-50 (opens in a new tab)

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 9 Jan 2026, 17:01 UTC

WeaknessesCWE-134

Technical details

References

Community reviews

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