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VulnerabilityPublished

CVE-2026-1664: agents · Insecure Direct Object Reference

Affects agentsSource CVE Database V5

0

Not known to be exploited · CVSS 6.9 Medium.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 4.0 base score
6.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 40% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 3 Feb 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
GitHubagentspkg:github/agentsOther threatsAffected
  • >=0.0.104 <=0.3.6
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

European organizations using Cloudflare Agents SDK version 0.0.104 should immediately upgrade to version agents@0.3.7, which includes fixes for this vulnerability. Beyond upgrading, developers should refactor their email routing logic to enforce strict identity boundaries, ensuring that routing decisions are based on cryptographically verified or origin-validated headers rather than untrusted external input. Implementing cryptographic signatures or token-based validation on email headers can prevent spoofing. Additionally, organizations should audit their use of Durable Objects in email processing to identify any unauthorized routing paths. Monitoring inbound email traffic for anomalous Message-ID or References header patterns can help detect exploitation attempts. Incorporating network-level protections such as email gateway filtering, SPF, DKIM, and DMARC enforcement will reduce the risk of header spoofing. Finally, organizations should review and update incident response plans to include scenarios involving email routing manipulation.

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

References

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