Vulnerability · Published Feb 3, 2026 · Assigned by cloudflare
CVE-2026-1664Insecure Direct Object Reference (IDOR) via Header-Based Email Routing
Medium 6.9
In plain English
A medium-severity authorization bypass via user-controlled key in agents. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 40% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 agents@0.3.7
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | agents | 0.3.7 | GHSA-r7x9-8ph7-w8cg |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| agents | 0.0.104 – through 0.3.6 |
Weakness: CWE-639 · 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