CyberSecBulletin
CVE-2025-66277NVD status: Analyzed

QTS: Improper Link Resolution Before File Access

Published Updated By the CyberSecBulletin desk

CVE-2025-66277 is a critical-severity improper link resolution before file access vulnerability in QTS from QNAP, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 5.2.8.3350 build 20251216 as the first without the flaw, so updating QTS to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.7% chance of exploitation within 30 days, higher than 54% of scored CVEs.

Patch this week

Critical severity: a successful attack would have severe impact.

What to do

  1. Update QTS to 5.2.8.3350 build 20251216 or a later version.
  2. Update QuTS hero to h5.3.2.3354 build 20251225 or h5.2.8.3350 build 20251216, whichever matches your release line, or a later version.
  3. Read the advisory on qnap.com for workarounds and exact fixed builds.
  4. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
QNAPQTS5.2.x up to, but not including, 5.2.8.3350 build 202512165.2.8.3350 build 20251216
QNAPQuTS heroh5.3.x up to, but not including, h5.3.2.3354 build 20251225; h5.2.x up to, but not including, h5.2.8.3350 build 20251216h5.3.2.3354 build 20251225, h5.2.8.3350 build 20251216

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 4.09.2CriticalCNA (qnapsecurity.com.tw)
CVSS 3.19.8CriticalNVD

Official description

A link following vulnerability has been reported to affect several QNAP operating system versions. The remote attackers can then exploit the vulnerability to traverse the file system to unintended locations. We have already fixed the vulnerability in the following versions: QTS 5.2.8.3350 build 20251216 and later QuTS hero h5.3.2.3354 build 20251225 and later QuTS hero h5.2.8.3350 build 20251216 and later

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Link Resolution Before File Access

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

How developers prevent this class of flaw

  • Follow the principle of least privilege when assigning access rights to entities in a software system. Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

More Improper Link Resolution Before File Access vulnerabilities (CWE-59)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in QTS

All QTS vulnerabilities

Recent Improper Link Resolution Before File Access vulnerabilities

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