CVE-2021-34357Network attack vector

Browser script execution via undisclosed reflected input

Published Nov 13, 2021 · Updated Sep 17, 2024

Reflected cross-site scripting in QNAP QmailAgent before 3.0.2 allows remote attackers to inject script through web requests. QNAP has not disclosed the affected endpoint, input parameter, or missing output-encoding operation responsible for the reflection. Exploitation requires user interaction and high-complexity conditions; injected script executes in the victim's browser and reads data or performs limited actions available to that session.

CVSS severity6.9
Medium
EPSS probability0.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected cross-site scripting in QNAP QmailAgent before 3.0.2 allows remote attackers to inject script through web requests. QNAP has not disclosed the affected endpoint, input parameter, or missing output-encoding operation responsible for the reflection. Exploitation requires user interaction and high-complexity conditions; injected script executes in the victim's browser and reads data or performs limited actions available to that session.

The record

CVE
CVE-2021-34357
Published
Nov 13, 2021
Updated
Sep 17, 2024
Vendor
Linn Products Limited
Product
QmailAgent
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record 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=unspecified <3.0.2 ( 2021/08/25 )

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Linn Products Limited · QmailAgentversion=unspecified <3.0.2 ( 2021/08/25 )

Published CVSS scores

6.9QNAP Systems, Inc.CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:L/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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