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Vulnerability details: VCID-hazd-1zmu-dubz
Vulnerability ID VCID-hazd-1zmu-dubz
Aliases CVE-2026-1664
GHSA-r7x9-8ph7-w8cg
Summary Summary 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 . Root cause The `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. Impact Insecure Direct Object Reference (IDOR) in email routing lets an attacker steer inbound mail to arbitrary Agent instances via spoofed Message-ID. Mitigation: * 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. * Agents-sdk users should upgrade to agents@0.3.7
Status Published
Exploitability 0.5
Weighted Severity 6.2
Risk 3.1
Affected and Fixed Packages Package Details
Weaknesses (3)
CWE-639 Authorization Bypass Through User-Controlled Key
CWE-937 OWASP Top Ten 2013 Category A9 - Using Components with Known Vulnerabilities
CWE-1035 OWASP Top Ten 2017 Category A9 - Using Components with Known Vulnerabilities
System Score Found at
epss 0.00023 https://api.first.org/data/v1/epss?cve=CVE-2026-1664
epss 0.00023 https://api.first.org/data/v1/epss?cve=CVE-2026-1664
epss 0.00023 https://api.first.org/data/v1/epss?cve=CVE-2026-1664
epss 0.00023 https://api.first.org/data/v1/epss?cve=CVE-2026-1664
cvssv3.1_qr MODERATE https://github.com/advisories/GHSA-r7x9-8ph7-w8cg
cvssv4 6.9 https://github.com/cloudflare/agents
generic_textual MODERATE https://github.com/cloudflare/agents
ssvc Track https://github.com/cloudflare/agents
cvssv4 6.9 https://github.com/cloudflare/agents/blob/main/docs/email.md
generic_textual MODERATE https://github.com/cloudflare/agents/blob/main/docs/email.md
cvssv3.1_qr MODERATE https://github.com/cloudflare/agents/security/advisories/GHSA-r7x9-8ph7-w8cg
cvssv4 6.9 https://github.com/cloudflare/agents/security/advisories/GHSA-r7x9-8ph7-w8cg
generic_textual MODERATE https://github.com/cloudflare/agents/security/advisories/GHSA-r7x9-8ph7-w8cg
cvssv4 6.9 https://nvd.nist.gov/vuln/detail/CVE-2026-1664
generic_textual MODERATE https://nvd.nist.gov/vuln/detail/CVE-2026-1664
Reference id Reference type URL
https://api.first.org/data/v1/epss?cve=CVE-2026-1664
https://github.com/cloudflare/agents/blob/main/docs/email.md
agents https://github.com/cloudflare/agents
CVE-2026-1664 https://nvd.nist.gov/vuln/detail/CVE-2026-1664
GHSA-r7x9-8ph7-w8cg https://github.com/advisories/GHSA-r7x9-8ph7-w8cg
GHSA-r7x9-8ph7-w8cg https://github.com/cloudflare/agents/security/advisories/GHSA-r7x9-8ph7-w8cg
No exploits are available.
Vector: 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 Found at https://github.com/cloudflare/agents
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

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Vector: SSVCv2/E:N/A:Y/T:P/P:M/B:A/M:M/D:T/2026-02-03T14:38:24Z/ Found at https://github.com/cloudflare/agents
Vector: 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 Found at https://github.com/cloudflare/agents/blob/main/docs/email.md
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

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Vector: 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 Found at https://github.com/cloudflare/agents/security/advisories/GHSA-r7x9-8ph7-w8cg
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

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physical

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Vector: 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 Found at https://nvd.nist.gov/vuln/detail/CVE-2026-1664
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

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none

passive

active

high

low

none

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Exploit Prediction Scoring System (EPSS)
Percentile 0.06737
EPSS Score 0.00023
Published At June 11, 2026, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2026-06-11T16:50:09.633104+00:00 Vulnrichment Import https://github.com/cisagov/vulnrichment/blob/develop/2026/1xxx/CVE-2026-1664.json 38.6.0