CVE-2016-5673
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 · uneditedUltraVNC Repeater before 1300 does not restrict destination IP addresses or TCP ports, which allows remote attackers to obtain open-proxy functionality by using a :: substring in between the IP address and port number.
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 · high confidenceUltraVNC Repeater versions before 1300 lack proper validation of destination IP addresses and TCP ports, allowing remote attackers to abuse it as an open proxy. The vulnerability is triggered by inserting a '::' substring between the target IP address and port number in the connection request, enabling the repeater to forward traffic to arbitrary destinations.
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<= 1201CVSS 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
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/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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Identify UltraVNC Repeater installationCheck for the presence of the UltraVNC Repeater executable (vnc_repeater.exe or repeater.exe) or service on the system. Common locations: C:\Program Files\UltraVNC\ or C:\Program Files (x86)\UltraVNC\Affected if UltraVNC Repeater is installed on the system
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Determine installed versionRight-click the repeater executable, select Properties, then look at the Version tab to find the File Version. Alternatively, check the version reported by the running service or check the executable file properties.Affected if The version is 1201 or lower (any version <= 1201)
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Verify network listener is activeCheck if the repeater is listening on its configured TCP port (default ports: 5500, 5900, or custom). Use command: netstat -an | findstr LISTENING or check via Resource Monitor.Affected if The repeater has an open TCP listener accepting connections from the network
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Confirm network exposureDetermine if the repeater's listener is bound to an IP address accessible from untrusted networks (0.0.0.0 or external IP) rather than localhost only. Check firewall rules and router forwarding configurations.Affected if The repeater port is reachable from untrusted/network-facing interfaces
A system is affected if UltraVNC Repeater version 1201 or lower is installed AND the service is listening on a network-accessible port.
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.
From vendor dataUpgrade UltraVNC Repeater to version 1300 or later which implements proper destination IP and port restrictions. If upgrading is not immediately possible, restrict network access to the repeater from untrusted sources via firewall rules.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2016-5673 — 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-2016-5673 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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