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Fencer Vulns
medium 5.5

CVE-2025-59529 json

Avahi: simple protocol server ignores accepts unlimited connections and logs failures without limit

published 2025-12-18 10 mo ago modified 2026-10-23 16 d ago also EUVD-2025-204402

cvss
5.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits
0
none known

Summary

Avahi is a system which facilitates service discovery on a local network via the mDNS/DNS-SD protocol suite. In versions up to and including 0.9-rc5, the simple protocol server ignores the documented client limit and accepts unlimited connections, allowing for easy local DoS. Although `CLIENTS_MAX` is defined, `server_work()` unconditionally `accept()`s and `client_new()` always appends the new client and increments `n_clients`. There is no check against the limit. When client cannot be accepted as a result of maximal socket number of avahi-daemon, it logs unconditionally error per each connection. Unprivileged local users can exhaust daemon memory and file descriptors, causing a denial of service system-wide for mDNS/DNS-SD. Exhausting local file descriptors causes increased system load caused by logging errors of each of request. Overloading prevents glibc calls using nss-mdns plugins to resolve `*.local.` names and link-local addresses. As of time of publication, no known patched versions are available, but a candidate fix is available in pull request 808, and some workarounds are available. Simple clients are offered for nss-mdns package functionality. It is not possible to disable the unix socket `/run/avahi-daemon/socket`, but resolution requests received via DBus are not affected directly. Tools avahi-resolve, avahi-resolve-address and avahi-resolve-host-name are not affected, they use DBus interface. It is possible to change permissions of unix socket after avahi-daemon is started. But avahi-daemon does not provide any configuration for it. Additional access restrictions like SELinux can also prevent unwanted tools to access the socket and keep resolution working for trusted users.

Patch / fix

  • avahi hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-ui hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-qt3 hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-qt4 hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-qt5 hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-glib hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-libs hummingbird 1 0.9~rc2-8.1.hum1
  • avahi-sharp hummingbird 1 0.9~rc2-8.1.hum1

red hat advisories RHSA-2026:7411

  • avahi Linux Micro 6.1 0.8-slfo.1.1_8.1
  • avahi Linux Micro 6.0 0.8-10.1
  • avahi SLE Module for Package Hub 15 SP7, SLE Module for Desktop Applications 15 SP7, SLE Module for Basesystem 15 SP7 0.8-150600.15.21.1
  • avahi-glib2 SLE Module for Desktop Applications 15 SP7, SLE Module for Basesystem 15 SP7 0.8-150600.15.21.1
  • avahi SLE Micro 5.5, SLE Micro 5.4, SLE Micro 5.3 0.8-150400.7.34.1
  • avahi SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 0.8-160000.6.1
  • avahi-glib2 SLES for SAP applications 16.0, SLES 16.0 0.8-160000.6.1
  • avahi SLES LTSS Extended Security 12 SP5 0.6.32-32.45.1

suse advisories SUSE-SU-2026:23161-1SUSE-SU-2026:23039-1SUSE-SU-2026:3218-1SUSE-SU-2026:3217-1SUSE-SU-2026:3216-1SUSE-SU-2026:22853-1

  • avahi openSUSE Leap 16.0 0.8-160000.6.1
  • avahi-qt6 openSUSE Leap 16.0 0.8-160000.6.1
  • avahi-glib2 openSUSE Leap 16.0 0.8-160000.6.1
  • avahi openSUSE Tumbleweed 0.8-45.1

opensuse advisories openSUSE-SU-2026:21417-1openSUSE-SU-2026:11313-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-59529 updated cvss 5.5

avahi: simple clients denial-of-service

  • Red Hat Enterprise Linux 6 avahi, avahi-ui, avahi-qt3, avahi-qt4, avahi-glib, avahi-libs, +7 more Red Hat Enterprise Linux 7 avahi, avahi-ui, avahi-qt3, avahi-qt4, avahi-glib, avahi-libs, +8 more Red Hat Enterprise Linux 8 avahi, avahi-ui, avahi-glib, avahi-libs, avahi-tools, avahi-autoipd, +5 more Red Hat Enterprise Linux 9 avahi, avahi-glib, avahi-libs, avahi-tools, avahi-autoipd, avahi-gobject, +2 more Red Hat Enterprise Linux 10 avahi Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images avahi 0.9~rc2-8.1.hum1, avahi-ui 0.9~rc2-8.1.hum1, avahi-qt3 0.9~rc2-8.1.hum1, avahi-qt4 0.9~rc2-8.1.hum1, avahi-qt5 0.9~rc2-8.1.hum1, avahi-glib 0.9~rc2-8.1.hum1, +11 more
    fixed: vendor fix RHSA-2026:7411

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
partial
Assessed
10 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/avahi/avahi/security/advisories/GHSA-73wf-3xmj-x82q referenced PoC, tagged "exploit" by a source, unverified
  • zeropath.com https://zeropath.com/blog/avahi-simple-protocol-server-dos-cve-2025-59529 referenced PoC, tagged "exploit" by a source, unverified
  • openwall.com http://www.openwall.com/lists/oss-security/2025/12/19/1 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • avahi avahi

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.