CVE-2021-34357
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedA cross-site scripting (XSS) vulnerability has been reported to affect QNAP device running QmailAgent. If exploited, this vulnerability allows remote attackers to inject malicious code. We have already fixed this vulnerability in the following versions of QmailAgent: QmailAgent 3.0.2 ( 2021/08/25 ) and later
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceCross-site scripting (XSS) vulnerability in QNAP QmailAgent allows remote attackers to inject malicious code. The vulnerability has a CVSS score of 6.1 (Medium), indicating it is exploitable but may require user interaction or specific conditions.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 3.0.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Verify QmailAgent is installedCheck if QmailAgent package exists on the QNAP system via App Center or by listing installed QNAP packages (use 'qpkg -l' or check /share/CACHEDEV1_DATA/.qpkg/QmailAgent if accessible)Affected if QmailAgent is not found on the system - not affected
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Determine installed QmailAgent versionOpen QmailAgent in QTS and navigate to Settings > About, or check the version via QNAP package management interface (App Center > QmailAgent > the version number displayed)Affected if Version shown is below 3.0.2 (e.g., 3.0.1, 3.0.0, or earlier)
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Confirm QmailAgent service is accessibleVerify the QmailAgent web interface is accessible by accessing https://[your-qnap-ip]:[port]/cgi-bin/qmailAgent (default port 8080 or configured port), or check if the service is running via QTS Resource MonitorAffected if Service is running and accessible - the XSS could potentially be triggered if the vulnerable code path is reachable
A system is affected if QmailAgent is installed and the installed version is lower than 3.0.2, and the QmailAgent service is accessible to potential attackers.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped3.0.2
Update QmailAgent to version 3.0.2 (released 2021/08/25) or later to remediate this vulnerability. No additional workarounds were described in the provided advisory.
QmailAgent 3.0.2
- Log into the QNAP device's QTS interface
- Navigate to App Center and search for QmailAgent
- Check for available updates or open QmailAgent settings
- Update QmailAgent to version 3.0.2 or later (released 2021/08/25)
- After updating, verify the installed version in the application settings
- Review email account configurations to ensure no malicious modifications were made prior to the update
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34357 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-34357 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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