CVE-2026-67546
Heym: Command execution via POST /api/mcp/fetch-tools stdio transport: supplied command is spawned before MCP validation
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.
Fixes and workarounds
No remediation reported in collected sources.
Missing remediation information is not evidence that no patch exists.
Affected products and versions
| Product | Versions | Authority |
|---|---|---|
| heym heymrun |
< 0.0.75 (affected) | CNA: GitHub_M |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 3.1 / 8.8 high |
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H | CNA: GitHub_M |
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-q589-34mvCNA: GitHub_M · x_refsource_CONFIRM
- https://github.com/heymrun/heym/commit/22b8ee60eb92128cf4ff04a9b6c0e1b62bf25a01CNA: GitHub_M · x_refsource_MISC
- https://github.com/heymrun/heym/commit/6c6213f88dfa8b2a70d23a9a271171241e910904CNA: GitHub_M · x_refsource_MISC
- https://github.com/heymrun/heym/releases/tag/v0.0.75CNA: GitHub_M · x_refsource_MISC
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