# CVE-2026-65957: Helio: Dashboard sideband CORS origin allowlist matches hostnames by prefix, admitting attacker-controlled origins in open mode

Status: published. Published: 2026-11-11. Updated: 2026-11-12.

Helio is an MCP proxy that sits between AI agents and the tools they use. Prior to version 0.8.0, the dashboard sideband (default 127.0.0.1:3100) validated CORS request origins by matching the hostname against a private-network string prefix (10., 172.16.–172.31., 192.168.) rather than validating an IP address. A public DNS name such as 192.168.attacker.com, 10.evil.io, or 172.16.pwn.example also satisfies that prefix, so the proxy echoed the attacker origin in Access-Control-Allow-Origin. This issue has been patched in version 0.8.0.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- gethelio / helio: < 0.8.0 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N; source: CNA: GitHub_M

- CVSS 4.0: 6.9 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: security-advisories@github.com

- CISA KEV: No listing in collected sources

- EPSS: 0.22% as of 2026-11-12; percentile 12.96%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-346, CWE-942

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/gethelio/helio/security/advisories/GHSA-2c3r-q7gv-hp2m (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/gethelio/helio/pull/121 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/gethelio/helio/commit/4ca8329c38b0edbc5e4d782a4e3b0cfc5cd7782e (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/gethelio/helio/releases/tag/v0.8.0 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/gethelio/helio/commit/4ca8329c38b0edbc5e4d782a4e3b0cfc5cd7782e (security-advisories@github.com)

- https://github.com/gethelio/helio/pull/121 (security-advisories@github.com)

- https://github.com/gethelio/helio/releases/tag/v0.8.0 (security-advisories@github.com)

- https://github.com/gethelio/helio/security/advisories/GHSA-2c3r-q7gv-hp2m (security-advisories@github.com)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-65957; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-65957; retrieved 2026-11-12; source updated 2026-11-11

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-65957; retrieved 2026-11-12; source updated Not reported

Revision: 9418a46cce1c6ce84d108180bd545b4e7a219066efb59c77807acae1bf92debd

Canonical: https://y2.dev/cve/CVE-2026-65957

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.