CVE-2026-21920

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style=\"background-color: rgb(255, 255, 255);\">A device is exposed to this issue when one of the following features are used / configurations are present:<br><br>- GeoIP:<br></span><tt><tt><tt></tt><br><tt><span style=\"background-color: rgb(255, 255, 255);\">[ security dynamic-address address-name &lt;name&gt; profile category GeoIP ... ]<br></span></tt></tt></tt><br><br>- DNS security:<br><br><tt><tt><tt><span style=\"background-color: rgb(255, 255, 255);\">[&nbsp;services security-metadata-streaming policy &lt;name&gt; dns detections ... ]<br><br>or<br><br>[ services security-intelligence profile &lt;profile-name&gt; category DNS ]<br>[ services security-intelligence profile policy &lt;policy-name&gt; DNS &lt;profile-name&gt; ]<br></span></tt><tt><tt><tt><br><tt>\n\n</tt></tt></tt><tt></tt><tt></tt><tt></tt><tt></tt><tt></tt><tt></tt></tt></tt></tt><tt></tt>"}], "value": "A device is exposed to this issue when one of the following features are used / configurations are present:\n\n- GeoIP:\n\n[ security dynamic-address address-name <name> profile category GeoIP ... ]\n\n\n- DNS security:\n\n[\u00a0services security-metadata-streaming policy <name> dns detections ... ]\n\nor\n\n[ services security-intelligence profile <profile-name> category DNS ]\n[ services security-intelligence profile policy <policy-name> DNS <profile-name> ]"}], "datePublic": "2026-01-14T17:00:00.000Z", "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<span style=\"background-color: rgb(255, 255, 255);\">An Unchecked Return Value vulnerability in the DNS module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).</span><br>\n\n<br><br>If an SRX Series device configured for DNS processing, receives a specifically formatted DNS request flowd will crash and restart, which causes a service interruption until the process has recovered.<br><br><p>This issue 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interruption until the process has recovered.\n\nThis issue affects Junos OS on SRX Series:\n\n\n\n * 23.4 versions before 23.4R2-S5,\n * 24.2 versions before 24.2R2-S1,\n * 24.4 versions before 24.4R2.\n\n\n\n\n\n\nThis issue does not affect Junos OS versions before 23.4R1.", "supportingMedia": [{"type": "text/html", "value": "<span style=\"background-color: rgb(255, 255, 255);\">An Unchecked Return Value vulnerability in the DNS module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).</span><br>\n\n<br><br>If an SRX Series device configured for DNS processing, receives a specifically formatted DNS request flowd will crash and restart, which causes a service interruption until the process has recovered.<br><br><p>This issue affects Junos OS on SRX Series:</p><p></p><ul><li>23.4 versions before 23.4R2-S5,</li><li>24.2 versions before 24.2R2-S1,</li><li>24.4 versions before 24.4R2.</li></ul><p></p>\n\n<p>This 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"cpe:2.3:h:juniper:srx4600:-:*:*:*:*:*:*:*", "matchCriteriaId": "56BA6B86-D3F4-4496-AE46-AC513C6560FA", "vulnerable": false}, {"criteria": "cpe:2.3:h:juniper:srx4700:-:*:*:*:*:*:*:*", "matchCriteriaId": "462CFD52-D3E2-4F7A-98AC-C589D2420556", "vulnerable": false}, {"criteria": "cpe:2.3:h:juniper:srx5400:-:*:*:*:*:*:*:*", "matchCriteriaId": "2FDDC897-747F-44DD-9599-7266F9B5B7B1", "vulnerable": false}, {"criteria": "cpe:2.3:h:juniper:srx5600:-:*:*:*:*:*:*:*", "matchCriteriaId": "68CA098D-CBE4-4E62-9EC0-43E1B6098710", "vulnerable": false}, {"criteria": "cpe:2.3:h:juniper:srx5800:-:*:*:*:*:*:*:*", "matchCriteriaId": "66F474D4-79B6-4525-983C-9A9011BD958B", "vulnerable": false}], "negate": false, "operator": "OR"}], "operator": "AND"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "An Unchecked Return Value vulnerability in the DNS module of Juniper Networks Junos OS on SRX Series allows an unauthenticated, network-based attacker to cause a Denial-of-Service (DoS).\n\n\n\n\nIf an SRX Series device configured for DNS processing, receives a specifically formatted DNS request flowd will crash and restart, which causes a service interruption until the process has recovered.\n\nThis issue affects Junos OS on SRX Series:\n\n\n\n * 23.4 versions before 23.4R2-S5,\n * 24.2 versions before 24.2R2-S1,\n * 24.4 versions before 24.4R2.\n\n\n\n\n\n\nThis issue does not affect Junos OS versions before 23.4R1."}, {"lang": "es", "value": "Una vulnerabilidad de valor de retorno no verificado en el m\u00f3dulo DNS de Juniper Networks Junos OS en la serie SRX permite a un atacante no autenticado y basado en la red causar una denegaci\u00f3n de servicio (DoS).\n\nSi un dispositivo de la serie SRX configurado para el procesamiento de DNS recibe una solicitud DNS espec\u00edficamente formateada, flowd se bloquear\u00e1 y reiniciar\u00e1, lo que causa una interrupci\u00f3n del servicio hasta que el proceso se haya recuperado.\n\nEste problema afecta a Junos OS en la serie SRX:\n\n * versiones 23.4 anteriores a 23.4R2-S5,\n * versiones 24.2 anteriores a 24.2R2-S1,\n * versiones 24.4 anteriores a 24.4R2.\n\nEste problema no afecta a las versiones de Junos OS anteriores a 23.4R1."}], "id": "CVE-2026-21920", "lastModified": "2026-06-17T10:19:09.987", "metrics": {"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": "sirt@juniper.net", "type": "Secondary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "YES", "Recovery": "AUTOMATIC", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 8.7, "baseSeverity": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "LOW", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:A/V:X/RE:M/U:X", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "MODERATE"}, "source": "sirt@juniper.net", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-21920", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-01-15T20:58:50.543674Z", "version": "2.0.3"}}]}, "published": "2026-01-15T21:16:08.217", "references": [{"source": "sirt@juniper.net", "tags": ["Vendor Advisory"], "url": "https://kb.juniper.net/JSA106020"}, {"source": "sirt@juniper.net", "tags": ["Vendor Advisory"], "url": "https://supportportal.juniper.net/JSA106020"}], "sourceIdentifier": "sirt@juniper.net", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-252"}], "source": "sirt@juniper.net", "type": "Secondary"}]}

{}

{"analysis": {"en": {"generated_at": "2026-04-18T19:10:57.723951+00:00", "value": {"mitigation_remediation": ["Upgrade each SRX device to Junos\u202fOS 23.4R2\u2011S5, 24.2R2\u2011S1, 24.4R2, 24.4R2\u2011S1, 25.2R1, or any newer release that includes the fix.", "Apply the same upgrade to all other SRX devices still running vulnerable Junos OS versions.", "Until the patch is deployed, consider restricting or filtering inbound DNS traffic from untrusted sources, or disabling the DNS service on SRX devices that do not require it."], "summary": {"action": "Patch", "impact": "Denial of Service"}, "threat_synthesis": {"affected_systems": "Juniper Networks Junos OS on SRX Series devices. Applications running on SRX1500, SRX1600, SRX2300, SRX300, SRX320, SRX340, SRX345, SRX380, SRX4100, SRX4120, SRX4200, SRX4300, SRX4600, SRX4700, SRX5400, SRX5600, SRX5800 are affected if they employ the DNS module. Versions of Junos OS before 23.4R1 are unaffected. The CVE notes that a service running version 23.4 before 23.4R2\u2011S5, 24.2 before 24.2R2\u2011S1, or 24.4 before 24.4R2 is vulnerable.", "description_and_impact": "A missing return value check in Juniper Networks Junos\u202fOS DNS processing causes a fault when flowd receives a specially crafted DNS request. The fault terminates the flowd process, which then restarts automatically. Since flowd is responsible for packet flow handling, the crash leads to a temporary loss of networking services on the affected SRX device, effectively denying connectivity until the process recovers. The vulnerability does not allow code execution or privilege escalation; its impact is limited to availability.", "risk_and_exploitability": "The CVSS score of 8.7 indicates a high\u2011severity availability flaw, but the EPSS score of less than 1% suggests a very low probability of exploitation in the wild. The vulnerability is not listed in the CISA KEV catalog, indicating that known exploits have not yet been observed or reported. Exploitation requires only network reachability to the device\u2019s DNS service; no authentication is necessary. An attacker could send the malformed DNS packet from any external source, cause a crash, and disrupt the SRX device\u2019s connectivity until the firewall recovers. The impact is a DoS of the device\u2019s flow handling subsystem, which can lead to loss of network services for affected customers."}}}}, "created": "2026-01-16T13:42:57.330492+00:00", "updated": "2026-04-18T19:15:10.614594+00:00", "vendors": ["juniper_networks", "juniper_networks$PRODUCT$junos_os"]}