CVE-2026-1664

What it is

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]

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

0.5% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-02-03 12:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 10:16 UTC Last updatedMost recent change to the record

Details

Published

2026-02-03 12:16 UTC

Last modified

2026-06-17 10:16 UTC

Exploit probability

0.5% · EPSS, next 30 days

Weakness

CWE-639 · Insecure direct object reference

Record status

Deferred

Attack profile CVSS 4.0 · 6.9

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

Low

Integrity

Low

Availability

None