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Medium, CVSS 6.9amended

Cloudflare Agents SDK has Insecure Direct Object Reference (IDOR) via Header-Based Email Routing

CVE-2026-1664GHSA-r7x9-8ph7-w8cg

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (agents 0.3.7), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm agents

    Affected
    < 0.3.7
    Fixed in
    0.3.7

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
6.9 · 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 · score source
EPSS
  • CVE-2026-1664: 0.46% estimated exploitation activity in the next 30 days; percentile 40.30 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary An Insecure Direct Object Reference (CWE-639) 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. Patches Agents-sdk users should upgrade to agents@0.3.7. PR: https://github.com/cloudflare/agents/pull/811 This documentation provides the necessary architectural…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-r7x9-8ph7-w8cg

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-r7x9-8ph7-w8cg

Agent brief

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# Patch Next advisory brief: CVE-2026-1664

Advisory: Cloudflare Agents SDK has Insecure Direct Object Reference (IDOR) via Header-Based Email Routing
IDs: CVE-2026-1664, GHSA-r7x9-8ph7-w8cg
Record: https://patchnext.com/advisories/cve-2026-1664 (revision 3, source checked 26 Oct 2026, 12:41 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: agents 0.3.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm agents: affected < 0.3.7; fixed in 0.3.7

## Suggested inspection (read-only)
- `npm ls agents --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on agents.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-r7x9-8ph7-w8cg (OSV record GHSA-r7x9-8ph7-w8cg lists affected ranges: npm agents >=0 <0.3.7 (fixed))
- Verified: https://github.com/advisories/GHSA-r7x9-8ph7-w8cg (GitHub-reviewed advisory GHSA-r7x9-8ph7-w8cg lists affected ranges: npm agents >=0 <0.3.7)

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