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CVE-2026-1664

Insecure Direct Object Reference (IDOR) via Header-Based Email Routing

Medium6.9EPSS 0.46%
Published
Updated
Reserved
Assigned by
cloudflare

Description

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 [email protected]

Scores

CVSS scores of CVE-2026-1664, by who scored it
Scored byCVSSScoreVector
cloudflareCNA (assigner)4.0Medium6.9CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N
NVDNVD · Deferred4.0Medium6.9CVSS: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
EPSS (exploitation in 30 days)
0.46% · top 60% of all CVEs (6 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: yes · Technical impact: partial
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The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 6.9.

Weakness

Affected products

  • agents

    • affected 0.0.104 – ≤ 0.3.6

Affected packages

From reviewed advisories of the GitHub Advisory Database.

References (1)

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .