CVE-2026-40691

{"id": "CVE-2026-40691", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-40691", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-22T14:30:33.327603Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "sep@nlnetlabs.nl", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 7.5, "attackVector": "NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 3.9}]}, "affected": [{"source": "sep@nlnetlabs.nl", "affectedData": [{"vendor": "NLnet Labs", "product": "Unbound", "versions": [{"status": "affected", "version": "1.9.0", "lessThan": "1.25.2", "versionType": "semver"}], "defaultStatus": "unaffected"}]}], "published": "2026-07-22T14:17:18.437", "references": [{"url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-40691.txt", "tags": ["Vendor Advisory"], "source": "sep@nlnetlabs.nl"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "sep@nlnetlabs.nl", "description": [{"lang": "en", "value": "CWE-122"}, {"lang": "en", "value": "CWE-787"}]}], "descriptions": [{"lang": "en", "value": "In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the routine that encrypts the reply in place fails to bound the reply length against the destination buffer size. The size clamp that protects the UDP path is not applied on the TCP path, so a reply larger than 65504 bytes is shifted forward by 48 bytes inside a buffer of capacity equal to 'msg-buffer-size', writing past the end of the heap allocation. A single malicious encrypted query crashes the resolver and lead to denial of service. This vulnerability needs Unbound to be compiled with DNSCrypt support ('--enable-dnscrypt') and the 'dnscrypt:' clause to be configured and enabled for the listening interfaces."}, {"lang": "es", "value": "En Unbound 1.9.0 hasta la versi\u00f3n 1.25.1 inclusive, cuando se recibe una consulta DNSCrypt a trav\u00e9s de TCP, la rutina que cifra la respuesta in situ no logra limitar la longitud de la respuesta con respecto al tama\u00f1o del b\u00fafer de destino. La restricci\u00f3n de tama\u00f1o que protege la ruta UDP no se aplica en la ruta TCP, por lo que una respuesta de m\u00e1s de 65504 bytes se desplaza 48 bytes hacia adelante dentro de un b\u00fafer con una capacidad igual a \u2019msg-buffer-size\u2019, escribiendo m\u00e1s all\u00e1 del final de la asignaci\u00f3n de memoria din\u00e1mica. Una \u00fanica consulta cifrada maliciosa bloquea el resolvedor y provoca una denegaci\u00f3n de servicio. Esta vulnerabilidad requiere que Unbound se compile con soporte para DNSCrypt (\u2019--enable-dnscrypt\u2019) y que la cl\u00e1usula \u2019dnscrypt:\u2019 est\u00e9 configurada y habilitada para las interfaces de escucha."}], "lastModified": "2026-10-24T13:10:00.147", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "2ED63F1A-AE65-4D9D-BC7E-1E674484BB80", "versionEndExcluding": "1.25.2", "versionStartIncluding": "1.9.0"}], "operator": "OR"}]}], "sourceIdentifier": "sep@nlnetlabs.nl"}