CVE-2026-1664 — agents
CVE-2026-1664 is a CWE-639 vulnerability in agents. A fix is available for agents — see the affected versions and patch details below.
Insecure Direct Object Reference (IDOR) via Header-Based Email Routing
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-1664.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
agentsnpmDescription
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 [email protected]. PR: https://github.com/cloudflare/agents/pull/811 This documentation provides the necessary architectural context for coding agents to mitigate the issue by refactoring the resolver to enforce strict identity boundaries.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | agents | all versions | 0.3.7npm install agents@0.3.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for agents, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update agents to 0.3.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-1664 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-1664 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-1664. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-1664 in your dependencies?
O3 Security finds CVE-2026-1664 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.