Vulnerability · Published Dec 18, 2025 · Assigned by GitHub_M
CVE-2025-59529Avahi: simple protocol server ignores accepts unlimited connections and logs failures without limit
Medium 5.5
In plain English
A medium-severity uncontrolled resource consumption in avahi from avahi. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities).
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | avahi | no fix listed | DEBIAN-CVE-2025-59529 |
| Debian:13 | avahi | no fix listed | DEBIAN-CVE-2025-59529 |
| Debian:14 | avahi | no fix listed | DEBIAN-CVE-2025-59529 |
| Ubuntu:22.04:LTS | avahi | no fix listed | UBUNTU-CVE-2025-59529 |
| Ubuntu:24.04:LTS | avahi | no fix listed | UBUNTU-CVE-2025-59529 |
| Ubuntu:25.10 | avahi | no fix listed | UBUNTU-CVE-2025-59529 |
| Ubuntu:26.04:LTS | avahi | no fix listed | UBUNTU-CVE-2025-59529 |
| Ubuntu:26.10 | avahi | no fix listed | UBUNTU-CVE-2025-59529 |
Affected products (as reported)
Weakness: CWE-400 · Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
References
- https://github.com/avahi/avahi/security/advisories/GHSA-73wf-3xmj-x82q x_refsource_CONFIRM
- https://github.com/avahi/avahi/pull/808 x_refsource_MISC
- https://github.com/avahi/avahi/pull/975 x_refsource_MISC
- https://zeropath.com/blog/avahi-simple-protocol-server-dos-cve-2025-59529 x_refsource_MISC
- http://www.openwall.com/lists/oss-security/2025/12/19/1