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Avahi DaemonApplication · Avahi

CVE-2009-0758

HIGH · 7.8 CVSS v2.0 Published 2009-03-03
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
87/100
Remediation priority · High
Remotely reachable No privileges 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
The originates_from_local_legacy_unicast_socket function in avahi-core/server.c in avahi-daemon 0.6.23 does not account for the network byte order of a port number when processing incoming multicast packets, which allows remote attackers to cause a denial of service (network bandwidth and CPU consumption) via a crafted legacy unicast mDNS query packet that triggers a multicast packet storm.

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 confidence

The originates_from_local_legacy_unicast_socket function in avahi-daemon 0.6.23 fails to account for network byte order of port numbers when processing incoming multicast packets. Remote attackers can send crafted legacy unicast mDNS query packets that cause the daemon to trigger a multicast packet storm, leading to excessive network bandwidth and CPU consumption.

MitigationUpgrade avahi-daemon to a patched version beyond 0.6.23, or implement network-level filtering to block suspicious legacy unicast mDNS queries.

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
Avahi DaemonApplication
Affected:= 0.6.23

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
Authentication
None
Confidentiality
None
Integrity
None
Availability
Complete

AV:N/AC:L/Au:N/C:N/I:N/A:C

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. Identify avahi-daemon version
    Run 'avahi-daemon --version' or check the installed package version using your system package manager (e.g., 'dpkg -l avahi-daemon' or 'rpm -qi avahi-daemon')
    Affected if The installed version is exactly 0.6.23
  2. Confirm avahi-daemon is running
    Check process status using 'ps aux | grep avahi-daemon' or 'systemctl status avahi-daemon'
    Affected if The avahi-daemon process is actively running
  3. Verify legacy unicast socket feature is active
    Examine avahi-daemon configuration files (typically in /etc/avahi/) for settings related to legacy unicast or legacy-unicast-socket, or inspect running configuration via 'avahi-daemon -k' with debug logging if available
    Affected if Legacy unicast socket handling is enabled in the configuration or runtime settings
  4. Monitor for packet storm symptoms
    Observe network interface traffic using tools like 'tcpdump' or 'iftop' to detect unusually high mDNS/multicast traffic originating from the local host
    Affected if Excessive outbound multicast mDNS traffic is observed relative to normal baseline

You are affected if avahi-daemon version 0.6.23 is running with legacy unicast socket handling enabled, and abnormal mDNS multicast traffic is detected.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade avahi-daemon to a patched version beyond 0.6.23, or implement network-level filtering to block suspicious legacy unicast mDNS queries.

Fix this in Avahi Daemon Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,380
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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-2009-0758 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
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