CVE-2026-55991

{"id": "CVE-2026-55991", "cveTags": [], "metrics": {"ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-55991", "role": "CISA Coordinator", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "version": "2.0.3", "timestamp": "2026-07-22T14:01:59.779165Z"}}], "cvssMetricV31": [{"type": "Secondary", "source": "sep@nlnetlabs.nl", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 5.9, "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H", "integrityImpact": "NONE", "userInteraction": "NONE", "attackComplexity": "HIGH", "availabilityImpact": "HIGH", "privilegesRequired": "NONE", "confidentialityImpact": "NONE"}, "impactScore": 3.6, "exploitabilityScore": 2.2}]}, "affected": [{"source": "sep@nlnetlabs.nl", "affectedData": [{"vendor": "NLnet Labs", "product": "Unbound", "versions": [{"status": "affected", "version": "1.22.0", "lessThan": "1.25.2", "versionType": "semver"}], "defaultStatus": "unaffected"}]}], "published": "2026-07-22T14:17:21.957", "references": [{"url": "https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-55991.txt", "tags": ["Vendor Advisory"], "source": "sep@nlnetlabs.nl"}], "vulnStatus": "Analyzed", "weaknesses": [{"type": "Secondary", "source": "sep@nlnetlabs.nl", "description": [{"lang": "en", "value": "CWE-195"}]}], "descriptions": [{"lang": "en", "value": "In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, a remote unauthenticated client can trigger a libngtcp2 assertion (if compiled with assertions on) and terminate the entire Unbound process using a single DNS-over-QUIC (DoQ) connection and one normal DNS query. This is caused by an erroneous error value passed to libngtcp2. When 'ngtcp2_conn_writev_stream()' returns 'NGTCP2_ERR_STREAM_DATA_BLOCKED', Unbound continues to call 'ngtcp2_ccerr_set_application_error()' with a '-1' error value. The 'int' literal '-1' is implicitly converted to the function's 'uint64_t error_code' parameter as '0xFFFFFFFFFFFFFFFF'. The follow-on 'ngtcp2_conn_write_connection_close()' serialises that value as a QUIC variable-length integer; because '2^64-1' exceeds the 62-bit varint ceiling, 'ngtcp2_put_uvarintlen()' fails 'assert(n < 4611686018427387904ULL)' and the whole resolver process aborts. A remote, unauthenticated DoQ client can trigger this deterministically with a single QUIC connection by advertising 'initial_max_stream_data_bidi_local = 1' in its transport parameters and sending one DoQ query without ever reading the stream."}, {"lang": "es", "value": "En NLnet Labs Unbound 1.22.0 hasta la versi\u00f3n 1.25.1 inclusive, un cliente remoto no autenticado puede activar una aserci\u00f3n de libngtcp2 (si se compila con aserciones activadas) y terminar todo el proceso de Unbound utilizando una \u00fanica conexi\u00f3n DNS-over-QUIC (DoQ) y una consulta DNS normal. Esto es causado por un valor de error err\u00f3neo pasado a libngtcp2. Cuando \u2019ngtcp2_conn_writev_stream()\u2019 devuelve \u2019NGTCP2_ERR_STREAM_DATA_BLOCKED\u2019, Unbound contin\u00faa llamando a \u2019ngtcp2_ccerr_set_application_error()\u2019 con un valor de error de \u2019-1\u2019. El literal \u2019int\u2019 \u2019-1\u2019 se convierte impl\u00edcitamente al par\u00e1metro \u2019uint64_t error_code\u2019 de la funci\u00f3n como \u20190xFFFFFFFFFFFFFFFF\u2019. La subsiguiente \u2019ngtcp2_conn_write_connection_close()\u2019 serializa ese valor como un entero de longitud variable QUIC; debido a que \u20192^64-1\u2019 excede el l\u00edmite de varint de 62 bits, \u2019ngtcp2_put_uvarintlen()\u2019 falla en \u2019assert(n < 4611686018427387904ULL)\u2019 y todo el proceso del resolvedor se aborta. Un cliente DoQ remoto no autenticado puede activar esto de forma determinista con una \u00fanica conexi\u00f3n QUIC al anunciar \u2019initial_max_stream_data_bidi_local = 1\u2019 en sus par\u00e1metros de transporte y enviando una consulta DoQ sin leer nunca el flujo."}], "lastModified": "2026-10-24T13:10:00.147", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "0C48102E-1D81-4A87-898D-F1CE83C78D26", "versionEndExcluding": "1.25.2", "versionStartIncluding": "1.22.0"}], "operator": "OR"}]}], "sourceIdentifier": "sep@nlnetlabs.nl"}