# CVE-2026-67546: Heym: Command execution via POST /api/mcp/fetch-tools stdio transport: supplied command is spawned before MCP validation

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

Heym builds and runs agentic systems and business-process automations on self-hosted infrastructure. Prior to version 0.0.75, the same POST /api/mcp/fetch-tools endpoint (any authenticated user, lowest role) also accepts the stdio transport, which spawns the attacker-supplied command with attacker-supplied args and an environment merged over os.environ. The process executes on the shared backend host before MCP protocol validation fails — so side effects fire regardless of whether the command speaks MCP. This is a distinct weakness class and exploit primitive from the SSRF (Advisory 2) on the same endpoint, and needs a different fix (role gating / opt-in trust boundary rather than egress controls). This issue has been patched in version 0.0.75.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- heymrun / heym: < 0.0.75 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-94

## Exploit evidence

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

## References

- https://github.com/heymrun/heym/security/advisories/GHSA-378x-q589-34mv (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/heymrun/heym/commit/22b8ee60eb92128cf4ff04a9b6c0e1b62bf25a01 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/heymrun/heym/commit/6c6213f88dfa8b2a70d23a9a271171241e910904 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/heymrun/heym/releases/tag/v0.0.75 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-67546; retrieved 2026-11-11; source updated 2026-11-11

Revision: b21565d3e77480377f2d52547aff07f2d46f3054b324b1cc8af3c0449fd2e6da

Canonical: https://y2.dev/cve/CVE-2026-67546

## Agent and API access

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- 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.