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Ssl Vpn ClientApplication · Synology

CVE-2021-47960

MEDIUM · 6.5 CVSS v3.1 Published 2026-04-10
Fix available
A fix is available. Upgrade to 1.4.5-0684 or later.
See remediation →
72/100
Remediation priority · Elevated
Remotely reachable No privileges

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
A files or directories accessible to external parties vulnerability in Synology SSL VPN Client before 1.4.5-0684 allows remote attackers to access files within the installation directory via a local HTTP server bound to the loopback interface. By leveraging user interaction with a crafted web page, attackers may retrieve sensitive files such as configuration files, certificates, and logs, leading to information disclosure.

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

Synology SSL VPN Client prior to version 1.4.5-0684 contains a local HTTP server bound to the loopback interface that allows remote attackers to access files within the installation directory through crafted web pages. By tricking users into visiting malicious websites, attackers can make the victim's browser send requests to the loopback-bound server and exfiltrate sensitive files including configuration files, certificates, and logs.

MitigationUpdate Synology SSL VPN Client to version 1.4.5-0684 or later to patch the insecure local HTTP server implementation. Additionally, educate users about risks of visiting untrusted websites to reduce the user interaction prerequisite.

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
Ssl Vpn ClientApplication
Affected:< 1.4.5-0684

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
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

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

  1. Verify Synology SSL VPN Client is installed
    Check for the presence of Synology SSL VPN Client software on the system. Look for installation directories or the application in system programs/features.
    Affected if The Synology SSL VPN Client software is found on the system
  2. Determine the installed version
    Access the application's version information through its UI, about section, or check the executable file properties to identify the exact version number.
    Affected if The installed version is lower than 1.4.5-0684
  3. Check if the SSL VPN Client service is running
    Look for the Synology SSL VPN Client process or service in the system's running processes or services list.
    Affected if The client service is actively running on the system
  4. Verify the local HTTP server is bound to loopback
    Use netstat or equivalent network tool to check for any HTTP server listening on 127.0.0.1 localhost interface associated with the Synology VPN client.
    Affected if A local HTTP server is listening on the loopback interface

A system is affected if Synology SSL VPN Client version below 1.4.5-0684 is installed and the vulnerable local HTTP server component is running.

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 1.4.5-0684 or later
Fixed in 1.4.5-0684
Interim mitigation

Update Synology SSL VPN Client to version 1.4.5-0684 or later to patch the insecure local HTTP server implementation. Additionally, educate users about risks of visiting untrusted websites to reduce the user interaction prerequisite.

Recommended fix High confidence

1.4.5-0684

  1. Download Synology SSL VPN Client version 1.4.5-0684 or later from the official Synology download center
  2. Uninstall the current version of Synology SSL VPN Client
  3. Install the updated version 1.4.5-0684
  4. Restart the system if prompted
  5. Verify the installation by checking the client version

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

Fix this in Ssl Vpn Client Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing1.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,090
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,744.

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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-2021-47960 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