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Antivirus EssentialApplication · Synology

CVE-2021-27648

HIGH · 8.8 CVSS v3.1 Published 2021-04-28
Fix available
A fix is available. Upgrade to 1.4.8-2801 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable Zero-click

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 · unedited
Externally controlled reference to a resource in another sphere in quarantine functionality in Synology Antivirus Essential before 1.4.8-2801 allows remote authenticated users to obtain privilege via unspecified vectors.

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 confidence

This is a privilege escalation vulnerability in Synology Antivirus Essential's quarantine functionality. The 'externally controlled reference to a resource in another sphere' classification indicates an Insecure Direct Object Reference (IDOR) or similar access control bypass where authenticated users can manipulate references to access resources or actions outside their intended权限. Affected versions before 1.4.8-2801 allow remote authenticated users to obtain elevated privileges via unspecified attack vectors.

MitigationUpgrade Synology Antivirus Essential to version 1.4.8-2801 or later. Review user access controls and monitor for any suspicious quarantine-related activity from authenticated user accounts.

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
Antivirus EssentialApplication
Affected:< 1.4.8-2801

CVSS 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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

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 checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Synology Antivirus Essential is installed
    Access the Synology DSM web interface, open Package Center, and look for Synology Antivirus Essential in the installed package list. Alternatively, run the command 'grep -i "Antivirus Essential" /var/packages/.package.list' or similar package listing command via SSH.
    Affected if The package is not installed, the vulnerability does not apply.
  2. Identify the installed version of Synology Antivirus Essential
    In DSM Package Center, click on Synology Antivirus Essential and view the version information displayed. Or via SSH, check the package info using 'cat /var/packages/AntivirusEssential/info.json' or 'synopkg list | grep -i antivirus'.
    Affected if Unable to determine the version - further manual investigation needed.
  3. Compare installed version against the affected range
    Check if the installed version is below 1.4.8-2801. The version string typically follows the format like '1.4.x-xxxx'. Compare the full version number including the build number after the hyphen.
    Affected if Installed version is 1.4.8-2801 or higher - the system is not vulnerable to this specific CVE.
  4. Verify quarantine functionality is accessible
    Log into DSM as an authenticated user (non-admin) and attempt to access the Antivirus Essential quarantine interface via the main menu or by navigating to the package. Check if quarantine-related features are visible and functional for standard users.
    Affected if Quarantine functionality is not accessible to standard users - the attack surface may be reduced but version check still applies.
  5. Review quarantine-related access logs
    Examine Synology DSM logs (Log Center) for any unusual quarantine operations, particularly actions performed by standard users that may indicate privilege escalation attempts. Look for quarantine delete, restore, or export actions from non-admin accounts.
    Affected if Standard user accounts are performing administrative quarantine operations - potential indicator of exploitation.

The environment is affected if Synology Antivirus Essential is installed with a version lower than 1.4.8-2801 and standard authenticated users can access quarantine functionality.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 1.4.8-2801 or later
Fixed in 1.4.8-2801
Interim mitigation

Upgrade Synology Antivirus Essential to version 1.4.8-2801 or later. Review user access controls and monitor for any suspicious quarantine-related activity from authenticated user accounts.

Recommended fix High confidence

1.4.8-2801 or later

  1. Log in to Synology DiskStation Manager (DSM) as an administrator
  2. Open Package Center
  3. Locate Synology Antivirus Essential in the installed packages
  4. Click on the package and select 'Update' to install the latest version
  5. Confirm the update to version 1.4.8-2801 or later
  6. Verify the installed version after the update completes

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Antivirus Essential Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,920
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-27648 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data