simple protocol server ignores accepts unlimited connections and logs failures without limit_CVE-2025-59529

{
    "lastseen": "",
    "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-rc2, 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.",
    "published": "2025-12-18T20:25:31.499Z",
    "modified": "2025-12-18T20:41:55.199Z",
    "type": "cve",
    "title": "simple protocol server ignores accepts unlimited connections and logs failures without limit",
    "source": "GitHub_M",
    "references": "https://github.com/avahi/avahi/security/advisories/GHSA-73wf-3xmj-x82q\nhttps://github.com/avahi/avahi/pull/808\nhttps://zeropath.com/blog/avahi-simple-protocol-server-dos-cve-2025-59529",
    "id": "CVE-2025-59529",
    "bulletinFamily": "",
    "cwe": [
        "CWE-400"
    ],
    "cvelist": null,
    "sourceData": "avahi avahi <= 0.9-rc2",
    "sourceHref": "",
    "cvss": {
        "score": 5.5,
        "severity": "MEDIUM",
        "vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
            "userInteraction": "",
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            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "avahi",
    "version": "<= 0.9-rc2",
    "vendor": "avahi",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}