CVE-2026-26240Public exploitNetwork attack vector

Service crash via unbounded filename copy

Published Jun 10, 2026 · Updated Jun 10, 2026

Stack-based buffer overflow in QNAP File Station 5 5.5.0 through 5.5.6.5242 allows remote attackers to crash its CGI service. The upload handler copies a multipart filename of 256 bytes or more into a fixed 256-byte stack buffer with strcpy, corrupting adjacent stack objects. Exploitation requires a low-privileged account with a writable directory, or a known share ID for a share with uploads enabled; demonstrated impact includes a service crash and stack-object corruption.

CVSS severity9.1
Critical
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack-based buffer overflow in QNAP File Station 5 5.5.0 through 5.5.6.5242 allows remote attackers to crash its CGI service. The upload handler copies a multipart filename of 256 bytes or more into a fixed 256-byte stack buffer with strcpy, corrupting adjacent stack objects. Exploitation requires a low-privileged account with a writable directory, or a known share ID for a share with uploads enabled; demonstrated impact includes a service crash and stack-object corruption.

The record

CVE
CVE-2026-26240
Published
Jun 10, 2026
Updated
Jun 10, 2026
Vendor
Linn Products Limited
Product
File Station 5
Classifications
CWE-121, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 10, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 10, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.5.0 <5.5.6.5243

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Linn Products Limited · File Station 5version=5.5.0 <5.5.6.5243

Published CVSS scores

1.3QNAP Systems, Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:U
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-121Stack-based Buffer Overflow
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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