CVE-2026-1664

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-1664", "assignerOrgId": "a22f1246-ba21-4bb4-a601-ad51614c1513", "state": "PUBLISHED", "assignerShortName": "cloudflare", "dateReserved": "2026-01-29T21:09:21.411Z", "datePublished": "2026-02-03T11:39:18.810Z", "dateUpdated": "2026-02-03T14:46:36.842Z"}, "containers": {"cna": {"affected": [{"collectionURL": "https://github.com/cloudflare/agents", "defaultStatus": "unaffected", "packageName": "agents", "repo": "https://github.com/cloudflare/agents", "versions": [{"lessThanOrEqual": "0.3.6", "status": "affected", "version": "0.0.104", "versionType": "semver"}]}], "credits": [{"lang": "en", "type": "reporter", "value": "asukalangley"}], "descriptions": [{"lang": "en", "supportingMedia": [{"base64": false, "type": "text/html", "value": "<b><p><span style=\"background-color: transparent;\">Summary</span></p></b><p>An Insecure Direct Object Reference has been found to exist in `createHeaderBasedEmailResolver()` function within the Cloudflare Agents SDK. The issue occurs because the `Message-ID` and `References` headers are parsed to derive the target agentName and agentId without proper validation or origin checks, allowing an external attacker with control of these headers to route inbound mail to arbitrary Durable Object instances and namespaces .</p><b><p><span style=\"background-color: transparent;\"><br></span></p><p><span style=\"background-color: transparent;\">Root cause</span></p></b><p><span style=\"background-color: transparent;\">The `</span><span style=\"background-color: transparent;\">createHeaderBasedEmailResolver()`</span><span style=\"background-color: transparent;\"> function lacks cryptographic verification or origin validation for the headers used in the routing logic, effectively allowing external input to dictate internal object routing.</span></p><b><p><span style=\"background-color: transparent;\"><br></span></p><p><span style=\"background-color: transparent;\">Impact</span></p></b><p><span style=\"background-color: transparent;\">Insecure Direct Object Reference (IDOR) in email routing lets an attacker steer inbound mail to arbitrary Agent instances via spoofed Message-ID.</span><br></p><p><span style=\"background-color: transparent;\"><br></span></p><p><span style=\"background-color: transparent;\"><b>Mitigation:</b></span></p><ul><li><span style=\"background-color: transparent;\">PR: </span><a target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/agents/pull/811\"><span style=\"background-color: transparent;\">https://github.com/cloudflare/agents/pull/811</span></a></li><li>This <a target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/agents/blob/main/docs/email.md\"><span style=\"background-color: transparent;\">documentation</span></a><span style=\"background-color: transparent;\">&nbsp;[<a target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/agents/blob/main/docs/email.md\">https://github.com/cloudflare/agents/blob/main/docs/email.md</a>] provides the necessary architectural context for coding agents to mitigate the issue by refactoring the resolver to enforce strict identity boundaries.</span></li><li>Agents-sdk users should upgrade to <span style=\"background-color: transparent;\">agents@0.3.7</span></li></ul><p></p><b></b>"}], "value": "Summary\n\nAn Insecure Direct Object Reference has been found to exist in `createHeaderBasedEmailResolver()` function within the Cloudflare Agents SDK. The issue occurs because the `Message-ID` and `References` headers are parsed to derive the target agentName and agentId without proper validation or origin checks, allowing an external attacker with control of these headers to route inbound mail to arbitrary Durable Object instances and namespaces .\n\n\n\n\nRoot cause\n\nThe `createHeaderBasedEmailResolver()` function lacks cryptographic verification or origin validation for the headers used in the routing logic, effectively allowing external input to dictate internal object routing.\n\n\n\n\nImpact\n\nInsecure Direct Object Reference (IDOR) in email routing lets an attacker steer inbound mail to arbitrary Agent instances via spoofed Message-ID.\n\n\n\n\n\nMitigation:\n\n * PR: https://github.com/cloudflare/agents/blob/main/docs/email.md ] provides the necessary architectural context for coding agents to mitigate the issue by refactoring the resolver to enforce strict identity boundaries.\n * Agents-sdk users should upgrade to agents@0.3.7"}], "metrics": [{"cvssV4_0": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "baseScore": 6.9, "baseSeverity": "MEDIUM", "exploitMaturity": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "LOW", "subIntegrityImpact": "LOW", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "problemTypes": [{"descriptions": [{"cweId": "CWE-639", "description": "CWE-639 Authorization Bypass Through User-Controlled Key", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"orgId": "a22f1246-ba21-4bb4-a601-ad51614c1513", "shortName": "cloudflare", "dateUpdated": "2026-02-03T11:45:10.068Z"}, "references": [{"url": "https://github.com/cloudflare/agents"}], "source": {"discovery": "UNKNOWN"}, "title": "Insecure Direct Object Reference (IDOR) via Header-Based Email Routing", "x_generator": {"engine": "Vulnogram 0.5.0"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-02-03T14:38:24.747542Z", "id": "CVE-2026-1664", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-02-03T14:46:36.842Z"}}]}}

{"dataType": "CVE_RECORD", "containers": {"adp": [{"title": "CISA ADP Vulnrichment", "metrics": [{"other": {"type": "ssvc", "content": {"id": "CVE-2026-1664", "role": "CISA Coordinator", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "version": "2.0.3", "timestamp": "2026-02-03T14:38:24.747542Z"}}}], "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-02-03T14:39:52.994Z"}}], "cna": {"title": "Insecure Direct Object Reference (IDOR) via Header-Based Email Routing", "source": {"discovery": "UNKNOWN"}, "credits": [{"lang": "en", "type": "reporter", "value": "asukalangley"}], "metrics": [{"format": "CVSS", "cvssV4_0": {"Safety": "NOT_DEFINED", "version": "4.0", "Recovery": "NOT_DEFINED", "baseScore": 6.9, "Automatable": "NOT_DEFINED", "attackVector": "NETWORK", "baseSeverity": "MEDIUM", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N", "exploitMaturity": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "userInteraction": "NONE", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "subIntegrityImpact": "LOW", "vulnIntegrityImpact": "LOW", "subAvailabilityImpact": "NONE", "vulnAvailabilityImpact": "NONE", "subConfidentialityImpact": "LOW", "vulnConfidentialityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "scenarios": [{"lang": "en", "value": "GENERAL"}]}], "affected": [{"repo": "https://github.com/cloudflare/agents", "versions": [{"status": "affected", "version": "0.0.104", "versionType": "semver", "lessThanOrEqual": "0.3.6"}], "packageName": "agents", "collectionURL": "https://github.com/cloudflare/agents", "defaultStatus": "unaffected"}], "references": [{"url": "https://github.com/cloudflare/agents"}], "x_generator": {"engine": "Vulnogram 0.5.0"}, "descriptions": [{"lang": "en", "value": "Summary\n\nAn Insecure Direct Object Reference has been found to exist in `createHeaderBasedEmailResolver()` function within the Cloudflare Agents SDK. The issue occurs because the `Message-ID` and `References` headers are parsed to derive the target agentName and agentId without proper validation or origin checks, allowing an external attacker with control of these headers to route inbound mail to arbitrary Durable Object instances and namespaces .\n\n\n\n\nRoot cause\n\nThe `createHeaderBasedEmailResolver()` function lacks cryptographic verification or origin validation for the headers used in the routing logic, effectively allowing external input to dictate internal object routing.\n\n\n\n\nImpact\n\nInsecure Direct Object Reference (IDOR) in email routing lets an attacker steer inbound mail to arbitrary Agent instances via spoofed Message-ID.\n\n\n\n\n\nMitigation:\n\n * PR: https://github.com/cloudflare/agents/blob/main/docs/email.md ] provides the necessary architectural context for coding agents to mitigate the issue by refactoring the resolver to enforce strict identity boundaries.\n * Agents-sdk users should upgrade to agents@0.3.7", "supportingMedia": [{"type": "text/html", "value": "<b><p><span style=\"background-color: transparent;\">Summary</span></p></b><p>An Insecure Direct Object Reference has been found to exist in `createHeaderBasedEmailResolver()` function within the Cloudflare Agents SDK. The issue occurs because the `Message-ID` and `References` headers are parsed to derive the target agentName and agentId without proper validation or origin checks, allowing an external attacker with control of these headers to route inbound mail to arbitrary Durable Object instances and namespaces .</p><b><p><span style=\"background-color: transparent;\"><br></span></p><p><span style=\"background-color: transparent;\">Root cause</span></p></b><p><span style=\"background-color: transparent;\">The `</span><span style=\"background-color: transparent;\">createHeaderBasedEmailResolver()`</span><span style=\"background-color: transparent;\"> function lacks cryptographic verification or origin validation for the headers used in the routing logic, effectively allowing external input to dictate internal object routing.</span></p><b><p><span style=\"background-color: transparent;\"><br></span></p><p><span style=\"background-color: transparent;\">Impact</span></p></b><p><span style=\"background-color: transparent;\">Insecure Direct Object Reference (IDOR) in email routing lets an attacker steer inbound mail to arbitrary Agent instances via spoofed Message-ID.</span><br></p><p><span style=\"background-color: transparent;\"><br></span></p><p><span style=\"background-color: transparent;\"><b>Mitigation:</b></span></p><ul><li><span style=\"background-color: transparent;\">PR: </span><a target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/agents/pull/811\"><span style=\"background-color: transparent;\">https://github.com/cloudflare/agents/pull/811</span></a></li><li>This <a target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/agents/blob/main/docs/email.md\"><span style=\"background-color: transparent;\">documentation</span></a><span style=\"background-color: transparent;\">&nbsp;[<a target=\"_blank\" rel=\"nofollow\" href=\"https://github.com/cloudflare/agents/blob/main/docs/email.md\">https://github.com/cloudflare/agents/blob/main/docs/email.md</a>] provides the necessary architectural context for coding agents to mitigate the issue by refactoring the resolver to enforce strict identity boundaries.</span></li><li>Agents-sdk users should upgrade to <span style=\"background-color: transparent;\">agents@0.3.7</span></li></ul><p></p><b></b>", "base64": false}]}], "problemTypes": [{"descriptions": [{"lang": "en", "type": "CWE", "cweId": "CWE-639", "description": "CWE-639 Authorization Bypass Through User-Controlled Key"}]}], "providerMetadata": {"orgId": "a22f1246-ba21-4bb4-a601-ad51614c1513", "shortName": "cloudflare", "dateUpdated": "2026-02-03T11:45:10.068Z"}}}, "cveMetadata": {"cveId": "CVE-2026-1664", "state": "PUBLISHED", "dateUpdated": "2026-02-03T14:46:36.842Z", "dateReserved": "2026-01-29T21:09:21.411Z", "assignerOrgId": "a22f1246-ba21-4bb4-a601-ad51614c1513", "datePublished": "2026-02-03T11:39:18.810Z", "assignerShortName": "cloudflare"}, "dataVersion": "5.2"}

{"affected": [{"affectedData": [{"collectionURL": "https://github.com/cloudflare/agents", "defaultStatus": "unaffected", "packageName": "agents", "repo": "https://github.com/cloudflare/agents", "versions": [{"lessThanOrEqual": "0.3.6", "status": "affected", "version": "0.0.104", "versionType": "semver"}]}], "source": "cna@cloudflare.com"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "Summary\n\nAn Insecure Direct Object Reference has been found to exist in `createHeaderBasedEmailResolver()` function within the Cloudflare Agents SDK. The issue occurs because the `Message-ID` and `References` headers are parsed to derive the target agentName and agentId without proper validation or origin checks, allowing an external attacker with control of these headers to route inbound mail to arbitrary Durable Object instances and namespaces .\n\n\n\n\nRoot cause\n\nThe `createHeaderBasedEmailResolver()` function lacks cryptographic verification or origin validation for the headers used in the routing logic, effectively allowing external input to dictate internal object routing.\n\n\n\n\nImpact\n\nInsecure Direct Object Reference (IDOR) in email routing lets an attacker steer inbound mail to arbitrary Agent instances via spoofed Message-ID.\n\n\n\n\n\nMitigation:\n\n * PR: https://github.com/cloudflare/agents/blob/main/docs/email.md ] provides the necessary architectural context for coding agents to mitigate the issue by refactoring the resolver to enforce strict identity boundaries.\n * Agents-sdk users should upgrade to agents@0.3.7"}, {"lang": "es", "value": "Resumen\n\nSe ha encontrado una Referencia Directa Insegura a Objeto que existe en la funci\u00f3n 'createHeaderBasedEmailResolver()' dentro del SDK de Cloudflare Agents. El problema ocurre porque los encabezados 'Message-ID' y 'References' se analizan para derivar el agentName y el agentId de destino sin la validaci\u00f3n adecuada o comprobaciones de origen, permitiendo a un atacante externo con control de estos encabezados enrutar el correo entrante a instancias y espacios de nombres arbitrarios de Durable Object.\n\nCausa ra\u00edz\n\nLa funci\u00f3n 'createHeaderBasedEmailResolver()' carece de verificaci\u00f3n criptogr\u00e1fica o validaci\u00f3n de origen para los encabezados utilizados en la l\u00f3gica de enrutamiento, permitiendo efectivamente que la entrada externa dicte el enrutamiento interno de objetos.\n\nImpacto\n\nLa Referencia Directa Insegura a Objeto (IDOR) en el enrutamiento de correo electr\u00f3nico permite a un atacante dirigir el correo entrante a instancias arbitrarias de Agent a trav\u00e9s de un Message-ID falsificado.\n\nMitigaci\u00f3n:\n\n * PR: https://github.com/cloudflare/agents/blob/main/docs/email.md ] proporciona el contexto arquitect\u00f3nico necesario para que los agentes de codificaci\u00f3n mitiguen el problema refactorizando el resolvedor para hacer cumplir l\u00edmites de identidad estrictos.\n * Los usuarios del SDK de Agents deben actualizar a agents@0.3.7"}], "id": "CVE-2026-1664", "lastModified": "2026-06-17T10:16:16.637", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 6.9, "baseSeverity": "MEDIUM", "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": "NONE", "subConfidentialityImpact": "LOW", "subIntegrityImpact": "LOW", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N/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:X/R:X/V:X/RE:X/U:X", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "cna@cloudflare.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-1664", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-02-03T14:38:24.747542Z", "version": "2.0.3"}}]}, "published": "2026-02-03T12:16:11.953", "references": [{"source": "cna@cloudflare.com", "url": "https://github.com/cloudflare/agents"}], "sourceIdentifier": "cna@cloudflare.com", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-639"}], "source": "cna@cloudflare.com", "type": "Secondary"}]}

{}

{"analysis": {"en": {"generated_at": "2026-04-18T00:22:38.493740+00:00", "value": {"mitigation_remediation": ["Upgrade the Cloudflare Agents SDK to version\u202f0.3.7 or later to apply the official fix for the IDOR issue.", "Refactor the createHeaderBasedEmailResolver according to the guidance in the project\u2019s email documentation, ensuring strict identity checks and, if possible, cryptographic verification of routing headers.", "Validate or sign inbound email headers before they influence routing logic; consider disabling email routing for services that do not require it or isolating the agents in a protected namespace."], "summary": {"action": "Update SDK", "impact": "Insecure Direct Object Reference enabling arbitrary routing of inbound mail to Agent instances"}, "threat_synthesis": {"affected_systems": "The vulnerability affects any deployment of the Cloudflare Agents SDK that uses the createHeaderBasedEmailResolver function, including versions prior to agents@0.3.7. Users of older or unpatched instances are at risk, regardless of the particular namespace or application configuration.", "description_and_impact": "A flaw in the Cloudflare Agents SDK\u2019s createHeaderBasedEmailResolver function parses the Message-ID and References headers without proper validation, allowing an attacker who controls those headers to specify any agentName or agentId. By spoofing these headers, the attacker can redirect inbound email traffic to arbitrary Durable Object instances or namespaces, potentially causing unsolicited processing, data exposure, or unintended command execution within those instances.", "risk_and_exploitability": "The CVSS base score is 6.9, indicating moderate severity. The EPSS score is below 1%, suggesting a very low probability of observed exploitation. The vulnerability is not listed in CISA\u2019s KEV catalog. Exploitation requires an attacker to send a crafted email with specific header values; therefore, the attack surface is limited to systems that accept inbound mail through the SDK\u2019s email routing logic."}}}}, "created": "2026-02-04T12:14:06.654743+00:00", "updated": "2026-04-18T00:30:25.710580+00:00", "vendors": ["cloudflare", "cloudflare$PRODUCT$agents_sdk"]}