CVE-2019-6477

{"containers": {"cna": {"affected": [{"product": "BIND9", "vendor": "ISC", "versions": [{"status": "affected", "version": "9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2, 9.14.1 -> 9.14.7, and versions 9.11.5-S6 -> 9.11.12-S1 of BIND 9 Supported Preview Edition. Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected"}]}], "datePublic": "2019-11-20T00:00:00.000Z", "descriptions": [{"lang": "en", "value": "With pipelining enabled each incoming query on a TCP connection requires a similar resource allocation to a query received via UDP or via TCP without pipelining enabled. A client using a TCP-pipelined connection to a server could consume more resources than the server has been provisioned to handle. When a TCP connection with a large number of pipelined queries is closed, the load on the server releasing these multiple resources can cause it to become unresponsive, even for queries that can be answered authoritatively or from cache. (This is most likely to be perceived as an intermittent server problem)."}], "metrics": [{"cvssV3_1": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}}], "problemTypes": [{"descriptions": [{"description": "By design, BIND is intended to limit the number of TCP clients that can be connected at any given time. The update to this functionality introduced by CVE-2018-5743 changed how BIND calculates the number of concurrent TCP clients from counting the outstanding TCP queries to counting the TCP client connections. On a server with TCP-pipelining capability, it is possible for one TCP client to send a large number of DNS requests over a single connection. Each outstanding query will be handled internally as an independent client request, thus bypassing the new TCP clients limit. 9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2, 9.14.1 -> 9.14.7, and versions 9.11.5-S6 -> 9.11.12-S1 of BIND 9 Supported Preview Edition. Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected.", "lang": "en", "type": "text"}]}], "providerMetadata": {"dateUpdated": "2020-10-20T11:06:38.000Z", "orgId": "404fd4d2-a609-4245-b543-2c944a302a22", "shortName": "isc"}, "references": [{"tags": ["x_refsource_CONFIRM"], "url": "https://kb.isc.org/docs/cve-2019-6477"}, {"tags": ["x_refsource_CONFIRM"], "url": "https://www.synology.com/security/advisory/Synology_SA_19_39"}, {"name": "FEDORA-2019-73a8737068", "tags": ["vendor-advisory", "x_refsource_FEDORA"], "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XGURMGQHX45KR4QDRCSUQHODUFOGNGAN/"}, {"tags": ["x_refsource_CONFIRM"], "url": "https://support.f5.com/csp/article/K15840535?utm_source=f5support&amp%3Butm_medium=RSS"}, {"name": "FEDORA-2019-c703d2304a", "tags": ["vendor-advisory", "x_refsource_FEDORA"], "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3DEMNZMKR57VQJCG5ZN55ZGTQRL2TFQ/"}, {"name": "DSA-4689", "tags": ["vendor-advisory", "x_refsource_DEBIAN"], "url": "https://www.debian.org/security/2020/dsa-4689"}, {"name": "openSUSE-SU-2020:1699", "tags": ["vendor-advisory", "x_refsource_SUSE"], "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html"}, {"name": "openSUSE-SU-2020:1701", "tags": ["vendor-advisory", "x_refsource_SUSE"], "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html"}], "solutions": [{"lang": "en", "value": "Upgrade to the patched release most closely related to your current version of BIND:\n\n BIND 9.11.13\n BIND 9.14.8\n BIND 9.15.6\n\nBIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.\n\n BIND 9.11.13-S1\n\nNote that the fix for CVE-2019-6477 addresses only the server memory leak issue. TCP-pipelining may still malfunction by dropping some responses on a TCP connection where a client query pattern generates excessive outstanding queries, but the malfunction will affect that TCP connection alone and will not cause any degradation of service to other clients. An affected client connection might also appear to hang, but will clear when either the client or the server initiates a close or reset and will not remain in that state indefinitely.\n\nDisabling TCP-pipelining entirely is completely effective at mitigating the vulnerability with minimal impact to clients that use pipelined TCP connections and with no impact to clients that do not support TCP-pipelining.\n\nThe majority of Internet client DNS queries are transported over UDP or TCP without use of TCP-pipelining."}], "source": {"discovery": "USER"}, "title": "TCP-pipelined queries can bypass tcp-clients limit", "workarounds": [{"lang": "en", "value": "The vulnerability can be avoided by disabling server TCP-pipelining:\n keep-response-order { any; };\nand then restarting BIND. The server restart is necessary because neither a 'reload' nor a 'reconfig' operation will properly reset currently pipelining TCP clients."}], "x_generator": {"engine": "Vulnogram 0.0.9"}, "x_legacyV4Record": {"CVE_data_meta": {"ASSIGNER": "security-officer@isc.org", "DATE_PUBLIC": "2019-11-20T19:49:00.000Z", "ID": "CVE-2019-6477", "STATE": "PUBLIC", "TITLE": "TCP-pipelined queries can bypass tcp-clients limit"}, "affects": {"vendor": {"vendor_data": [{"product": {"product_data": [{"product_name": "BIND9", "version": {"version_data": [{"version_value": "9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2, 9.14.1 -> 9.14.7, and versions 9.11.5-S6 -> 9.11.12-S1 of BIND 9 Supported Preview Edition. Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected"}]}}]}, "vendor_name": "ISC"}]}}, "data_format": "MITRE", "data_type": "CVE", "data_version": "4.0", "description": {"description_data": [{"lang": "eng", "value": "With pipelining enabled each incoming query on a TCP connection requires a similar resource allocation to a query received via UDP or via TCP without pipelining enabled. A client using a TCP-pipelined connection to a server could consume more resources than the server has been provisioned to handle. When a TCP connection with a large number of pipelined queries is closed, the load on the server releasing these multiple resources can cause it to become unresponsive, even for queries that can be answered authoritatively or from cache. (This is most likely to be perceived as an intermittent server problem)."}]}, "generator": {"engine": "Vulnogram 0.0.9"}, "impact": {"cvss": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}}, "problemtype": {"problemtype_data": [{"description": [{"lang": "eng", "value": "By design, BIND is intended to limit the number of TCP clients that can be connected at any given time. The update to this functionality introduced by CVE-2018-5743 changed how BIND calculates the number of concurrent TCP clients from counting the outstanding TCP queries to counting the TCP client connections. On a server with TCP-pipelining capability, it is possible for one TCP client to send a large number of DNS requests over a single connection. Each outstanding query will be handled internally as an independent client request, thus bypassing the new TCP clients limit. 9.11.6-P1 -> 9.11.12, 9.12.4-P1 -> 9.12.4-P2, 9.14.1 -> 9.14.7, and versions 9.11.5-S6 -> 9.11.12-S1 of BIND 9 Supported Preview Edition. Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected."}]}]}, "references": {"reference_data": [{"name": "https://kb.isc.org/docs/cve-2019-6477", "refsource": "CONFIRM", "url": "https://kb.isc.org/docs/cve-2019-6477"}, {"name": "https://www.synology.com/security/advisory/Synology_SA_19_39", "refsource": "CONFIRM", "url": "https://www.synology.com/security/advisory/Synology_SA_19_39"}, {"name": "FEDORA-2019-73a8737068", "refsource": "FEDORA", "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/XGURMGQHX45KR4QDRCSUQHODUFOGNGAN/"}, {"name": "https://support.f5.com/csp/article/K15840535?utm_source=f5support&utm_medium=RSS", "refsource": "CONFIRM", "url": "https://support.f5.com/csp/article/K15840535?utm_source=f5support&utm_medium=RSS"}, {"name": "FEDORA-2019-c703d2304a", "refsource": "FEDORA", "url": "https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/L3DEMNZMKR57VQJCG5ZN55ZGTQRL2TFQ/"}, {"name": "DSA-4689", "refsource": "DEBIAN", "url": "https://www.debian.org/security/2020/dsa-4689"}, {"name": "openSUSE-SU-2020:1699", "refsource": "SUSE", "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html"}, {"name": "openSUSE-SU-2020:1701", "refsource": "SUSE", "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html"}]}, "solution": [{"lang": "en", "value": "Upgrade to the patched release most closely related to your current version of BIND:\n\n BIND 9.11.13\n BIND 9.14.8\n BIND 9.15.6\n\nBIND Supported Preview Edition is a special feature preview branch of BIND provided to eligible ISC support customers.\n\n BIND 9.11.13-S1\n\nNote that the fix for CVE-2019-6477 addresses only the server memory leak issue. TCP-pipelining may still malfunction by dropping some responses on a TCP connection where a client query pattern generates excessive outstanding queries, but the malfunction will affect that TCP connection alone and will not cause any degradation of service to other clients. An affected client connection might also appear to hang, but will clear when either the client or the server initiates a close or reset and will not remain in that state indefinitely.\n\nDisabling TCP-pipelining entirely is completely effective at mitigating the vulnerability with minimal impact to clients that use pipelined TCP connections and with no impact to clients that do not support TCP-pipelining.\n\nThe majority of Internet client DNS queries are transported over UDP or TCP without use of TCP-pipelining."}], "source": {"discovery": "USER"}, "work_around": [{"lang": "en", "value": "The vulnerability can be avoided by disabling server TCP-pipelining:\n keep-response-order { any; };\nand then restarting BIND. The server restart is necessary because neither a 'reload' nor a 'reconfig' operation will properly reset currently pipelining TCP clients."}]}}, "adp": [{"providerMetadata": {"orgId": "af854a3a-2127-422b-91ae-364da2661108", "shortName": "CVE", "dateUpdated": "2024-08-04T20:23:21.464Z"}, "title": "CVE Program Container", "references": [{"tags": ["x_refsource_CONFIRM", "x_transferred"], "url": "https://kb.isc.org/docs/cve-2019-6477"}, {"tags": ["x_refsource_CONFIRM", "x_transferred"], "url": "https://www.synology.com/security/advisory/Synology_SA_19_39"}, {"name": "FEDORA-2019-73a8737068", "tags": ["vendor-advisory", "x_refsource_FEDORA", "x_transferred"], "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XGURMGQHX45KR4QDRCSUQHODUFOGNGAN/"}, {"tags": ["x_refsource_CONFIRM", "x_transferred"], "url": "https://support.f5.com/csp/article/K15840535?utm_source=f5support&amp%3Butm_medium=RSS"}, {"name": "FEDORA-2019-c703d2304a", "tags": ["vendor-advisory", "x_refsource_FEDORA", "x_transferred"], "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3DEMNZMKR57VQJCG5ZN55ZGTQRL2TFQ/"}, {"name": "DSA-4689", "tags": ["vendor-advisory", "x_refsource_DEBIAN", "x_transferred"], "url": "https://www.debian.org/security/2020/dsa-4689"}, {"name": "openSUSE-SU-2020:1699", "tags": ["vendor-advisory", "x_refsource_SUSE", "x_transferred"], "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html"}, {"name": "openSUSE-SU-2020:1701", "tags": ["vendor-advisory", "x_refsource_SUSE", "x_transferred"], "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html"}]}]}, "cveMetadata": {"assignerOrgId": "404fd4d2-a609-4245-b543-2c944a302a22", "assignerShortName": "isc", "cveId": "CVE-2019-6477", "datePublished": "2019-11-26T16:11:16.500Z", "dateReserved": "2019-01-16T00:00:00.000Z", "dateUpdated": "2024-09-16T16:47:45.899Z", "state": "PUBLISHED"}, "dataType": "CVE_RECORD", "dataVersion": "5.1"}

{}

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Versions 9.15.0 -> 9.15.5 of the BIND 9.15 development branch are also affected"}]}], "source": "security-officer@isc.org"}], "configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*", "matchCriteriaId": "D4D32184-BCD1-4459-8ACA-45B720B72482", "versionEndIncluding": "9.11.12", "versionStartIncluding": "9.11.7", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*", "matchCriteriaId": "A58BC6C1-84DF-4EF1-8B51-9F2C51784C78", "versionEndIncluding": "9.14.7", "versionStartIncluding": "9.14.1", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:*:*:*:*:*:*:*:*", "matchCriteriaId": "8889BE5E-3E97-401A-BC81-082F77F72576", "versionEndIncluding": "9.15.5", "versionStartIncluding": "9.15.0", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:9.11.5:s6:*:*:supported_preview:*:*:*", "matchCriteriaId": "46E6A4BD-D69B-4A70-821D-5612DD1315EF", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:9.11.6:p1:*:*:*:*:*:*", "matchCriteriaId": "588F49CE-64D1-4073-928F-88D2AE5C0AB4", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:9.11.6:rc1:*:*:*:*:*:*", "matchCriteriaId": "31FE272C-24BC-4B67-A664-D29F595E7071", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:9.11.12:s1:*:*:supported_preview:*:*:*", "matchCriteriaId": "3CABCB08-B838-45F7-AA87-77C6B8767DD0", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:9.12.4:p1:*:*:*:*:*:*", "matchCriteriaId": "E121D018-42B7-467E-9481-EDA4021401AF", "vulnerable": true}, {"criteria": "cpe:2.3:a:isc:bind:9.12.4:p2:*:*:*:*:*:*", "matchCriteriaId": "343890F9-D6B4-433C-9131-9526DBB75749", "vulnerable": true}], "negate": false, "operator": "OR"}]}, {"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:fedoraproject:fedora:30:*:*:*:*:*:*:*", "matchCriteriaId": "97A4B8DF-58DA-4AB6-A1F9-331B36409BA3", "vulnerable": true}, {"criteria": "cpe:2.3:o:fedoraproject:fedora:31:*:*:*:*:*:*:*", "matchCriteriaId": "80F0FA5D-8D3B-4C0E-81E2-87998286AF33", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "With pipelining enabled each incoming query on a TCP connection requires a similar resource allocation to a query received via UDP or via TCP without pipelining enabled. A client using a TCP-pipelined connection to a server could consume more resources than the server has been provisioned to handle. When a TCP connection with a large number of pipelined queries is closed, the load on the server releasing these multiple resources can cause it to become unresponsive, even for queries that can be answered authoritatively or from cache. (This is most likely to be perceived as an intermittent server problem)."}, {"lang": "es", "value": "Con pipelining habilitada, cada consulta entrante en una conexi\u00f3n TCP requiere una asignaci\u00f3n de recursos similar a una consulta recibida por medio de UDP o TCP sin pipelining habilitada. Un cliente que utiliza una conexi\u00f3n canalizada por TCP a un servidor podr\u00eda consumir m\u00e1s recursos de los que el servidor ha sido provisionado para manejar. Cuando una conexi\u00f3n TCP con un gran n\u00famero de consultas canalizadas se cierra, la carga en el servidor que libera estos m\u00faltiples recursos puede causar que no responda, inclusive para consultas que pueden ser respondidas con autoridad o desde la memoria cach\u00e9. (Esto es muy probable que sea percibido como un problema de servidor intermitente)."}], "id": "CVE-2019-6477", "lastModified": "2026-06-17T02:39:06.963", "metrics": {"cvssMetricV2": [{"acInsufInfo": false, "baseSeverity": "MEDIUM", "cvssData": {"accessComplexity": "LOW", "accessVector": "NETWORK", "authentication": "NONE", "availabilityImpact": "PARTIAL", "baseScore": 5.0, "confidentialityImpact": "NONE", "integrityImpact": "NONE", "vectorString": "AV:N/AC:L/Au:N/C:N/I:N/A:P", "version": "2.0"}, "exploitabilityScore": 10.0, "impactScore": 2.9, "obtainAllPrivilege": false, "obtainOtherPrivilege": false, "obtainUserPrivilege": false, "source": "nvd@nist.gov", "type": "Primary", "userInteractionRequired": false}], "cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "security-officer@isc.org", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 3.6, "source": "nvd@nist.gov", "type": "Primary"}]}, "published": "2019-11-26T16:15:13.963", "references": [{"source": "security-officer@isc.org", "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html"}, {"source": "security-officer@isc.org", "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html"}, {"source": "security-officer@isc.org", "tags": ["Third Party Advisory"], "url": "https://kb.isc.org/docs/cve-2019-6477"}, {"source": "security-officer@isc.org", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3DEMNZMKR57VQJCG5ZN55ZGTQRL2TFQ/"}, {"source": "security-officer@isc.org", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XGURMGQHX45KR4QDRCSUQHODUFOGNGAN/"}, {"source": "security-officer@isc.org", "url": "https://support.f5.com/csp/article/K15840535?utm_source=f5support&amp%3Butm_medium=RSS"}, {"source": "security-officer@isc.org", "url": "https://www.debian.org/security/2020/dsa-4689"}, {"source": "security-officer@isc.org", "tags": ["Third Party Advisory"], "url": "https://www.synology.com/security/advisory/Synology_SA_19_39"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00041.html"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00044.html"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Third Party Advisory"], "url": "https://kb.isc.org/docs/cve-2019-6477"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/L3DEMNZMKR57VQJCG5ZN55ZGTQRL2TFQ/"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XGURMGQHX45KR4QDRCSUQHODUFOGNGAN/"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://support.f5.com/csp/article/K15840535?utm_source=f5support&amp%3Butm_medium=RSS"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "url": "https://www.debian.org/security/2020/dsa-4689"}, {"source": "af854a3a-2127-422b-91ae-364da2661108", "tags": ["Third Party Advisory"], "url": "https://www.synology.com/security/advisory/Synology_SA_19_39"}], "sourceIdentifier": "security-officer@isc.org", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-400"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"acknowledgement": "Red Hat would like to thank ISC for reporting this issue.", "affected_release": [{"advisory": "RHSA-2020:1061", "cpe": "cpe:/o:redhat:enterprise_linux:7", "package": "bind-32:9.11.4-16.P2.el7", "product_name": "Red Hat Enterprise Linux 7", "release_date": "2020-03-31T00:00:00Z"}, {"advisory": "RHSA-2020:1845", "cpe": "cpe:/a:redhat:enterprise_linux:8", "package": "bind-32:9.11.13-3.el8", "product_name": "Red Hat Enterprise Linux 8", "release_date": "2020-04-28T00:00:00Z"}, {"advisory": "RHSA-2020:1845", "cpe": "cpe:/o:redhat:enterprise_linux:8", "package": "bind-32:9.11.13-3.el8", "product_name": "Red Hat Enterprise Linux 8", "release_date": "2020-04-28T00:00:00Z"}], "bugzilla": {"description": "bind: TCP Pipelining doesn't limit TCP clients on a single connection", "id": "1773617", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=1773617"}, "csaw": false, "cvss3": {"cvss3_base_score": "7.5", "cvss3_scoring_vector": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "status": "verified"}, "cwe": "CWE-400", "details": ["With pipelining enabled each incoming query on a TCP connection requires a similar resource allocation to a query received via UDP or via TCP without pipelining enabled. A client using a TCP-pipelined connection to a server could consume more resources than the server has been provisioned to handle. When a TCP connection with a large number of pipelined queries is closed, the load on the server releasing these multiple resources can cause it to become unresponsive, even for queries that can be answered authoritatively or from cache. (This is most likely to be perceived as an intermittent server problem).", "A flaw was found in the way bind limited the number of TCP clients that can be connected at any given time. A remote attacker could use one TCP client to send a large number of DNS requests over a single connection, causing exhaustion of the pool of file descriptors available to named, and potentially affecting network connections and the management of files such as log files or zone journal files."], "mitigation": {"lang": "en:us", "value": "The vulnerability can be mitigated by disabling server TCP-pipelining:\n~~~\nkeep-response-order { any; };\n~~~\nand then restarting BIND. The server restart is necessary because neither a 'reload' nor a 'reconfig' operation will properly reset currently pipelining TCP clients.\nDisabling TCP-pipelining entirely is completely effective at mitigating the vulnerability with minimal impact to clients that use pipelined TCP connections and with no impact to clients that do not support TCP-pipelining. The majority of Internet client DNS queries are transported over UDP or TCP without use of TCP-pipelining.\nNote: This mitigation will only work with bind-9.11 and above."}, "name": "CVE-2019-6477", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:5", "fix_state": "Not affected", "package_name": "bind", "product_name": "Red Hat Enterprise Linux 5"}, {"cpe": "cpe:/o:redhat:enterprise_linux:5", "fix_state": "Not affected", "package_name": "bind97", "product_name": "Red Hat Enterprise Linux 5"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "bind", "product_name": "Red Hat Enterprise Linux 6"}], "public_date": "2019-11-20T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2019-6477\nhttps://nvd.nist.gov/vuln/detail/CVE-2019-6477\nhttps://kb.isc.org/docs/cve-2019-6477"], "statement": "The patch for CVE-2018-5743 introduced a change in the way bind calculated the number of concurrent connections, from counting the outstanding TCP queries to counting the TCP client connections. However this functionality was not correctly implemented, a attacker could use a single TCP connection to send large number of DNS requests causing denial of service. As per upstream the fix does not help in a situation where a TCP-pipelining client is sending queries at an excessive rate, allowing a backlog of outstanding queries to build up. More details about this is available in the upstream advisory.\nThis bind flaw can be exploited by a remote attacker (AV:N) by opening large number of simultaneous TCP client connections with the server. The attacker needs to use a server which has TCP-pipelining capability to use one TCP connection to send large number of requests. (AC:L and PR:N) No user interaction is required from the server side (UI:N). The attacker can cause denial of service (A:H) by exhausting the file descriptor pool which named has access to. (S:U)", "threat_severity": "Moderate"}

{}