CVE-2025-59529 Avahi: simple protocol server ignores accepts unlimited connections and logs failures without limit

What is CVE-2025-59529?

CVE-2025-59529 is a medium-severity denial of service vulnerability in avahi, published on 18 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

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.

Weakness: CWE-400

Which versions are affected by CVE-2025-59529?

It affects 1 product.

Products include Avahi Avahi.

How do I fix CVE-2025-59529?

No fix published yet.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2025-59529 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-59529 exists.

Other vulnerabilities in avahi

• CVE-2017-6519 Denial of service in n/a Critical 9.1
• CVE-2021-26720 Path traversal in n/a High 7.8
• CVE-2026-24401 Avahi has Uncontrolled Recursion in lookup_handle_cname function Medium 6.5
• CVE-2025-68468 Avahi has a reachable assertion in lookup_multicast_callback Medium 6.5
• CVE-2025-68471 Avahi has a reachable assertion in lookup_start Medium 6.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-72851, AZL-72853, BELL-CVE-2025-59529, CLSA-2026-1786360814, DEBIAN-CVE-2025-59529, ECHO-7e9e-9ac7-d59b and 14 more.