CVE-2015-2809
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 · uneditedThe Multicast DNS (mDNS) responder in Synology DiskStation Manager (DSM) before 3.1 inadvertently responds to unicast queries with source addresses that are not link-local, which allows remote attackers to cause a denial of service (traffic amplification) or obtain potentially sensitive information via port-5353 UDP packets to the Avahi component.
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 confidenceThe mDNS responder in Synology DSM before version 3.1 incorrectly processes unicast queries received from non-link-local (remote) IP addresses on port 5353/UDP. Properly, mDNS should only respond to queries from the link-local multicast address 224.0.0.251 on the local network. This misconfiguration allows remote attackers to trigger responses, enabling traffic amplification for denial of service or potential information disclosure.
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<= 3.0CVSS 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
- Authentication
- None
- Confidentiality
- Partial
- Integrity
- None
- Availability
- None
AV:N/AC:L/Au:N/C:P/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 checksWork through these to decide whether this CVE applies to you.
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Verify Synology DSM versionCheck the installed DSM version via the web interface (Control Panel > Info Center) or by running 'cat /etc/VERSION' on the command lineAffected if The DSM version is 3.0 or earlier, or any version prior to 3.1
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Confirm mDNS responder is runningCheck if the Avahi daemon or Synology mDNS responder process is active: run 'ps | grep -i avahi' or 'ps | grep -i mdns' on the command lineAffected if The mDNS responder process is running (the vulnerability only applies when the service is active)
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Verify port 5353/UDP is listeningCheck if port 5353 is open and listening: run 'netstat -ulnp | grep 5353' or 'ss -ulnp | grep 5353'Affected if Port 5353/UDP is bound to a listening service (exposure requires the port to be accessible)
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Test mDNS behavior from remote sourceSend a unicast mDNS query from a non-link-local (remote) IP address to the DSM system on port 5353/UDP and observe if a response is generatedAffected if The system responds to unicast mDNS queries originating from IP addresses outside the 224.0.0.0/24 link-local range
A user is affected if running Synology DSM version 3.0 or earlier with the mDNS responder active and responding to unicast queries from non-link-local source addresses on port 5353/UDP.
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 dataConfigure the Avahi/mDNS responder to ignore unicast queries from non-link-local source addresses, restricting responses to legitimate link-local multicast queries only.
- Consultation1.0 h
- Implementation1.0 h
- Testing1.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2015-2809 — 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-2015-2809 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
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- Version or environment caveats, and links to real fixes
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