GHSA-wv94-5qcp-6m36

Summary

The PraisonAI MCP HTTP-stream server creates a new in-memory session on every initialize request and never removes it. The cleanup routine that would expire sessions (_cleanup_sessions) is defined but never called anywhere in the codebase, and the configured session TTL is never enforced. There is no cap on the number of sessions. Because initialize requires no authentication and the server keeps every session dictionary forever, an attacker who can reach the endpoint (directly when the server is bound to a routable address, or from a victim's browser via the separate Origin-validation bypass) can drive memory usage up without bound until the process is killed by the out-of-memory killer. The same unbounded-growth pattern also applies to the cancelled-requests set populated by notifications/cancelled.

Details

In transports/http_stream.py, each initialize creates and stores a session with no limit:

if body.get("method") == "initialize":
    new_session_id = str(uuid.uuid4())
    self._sessions[new_session_id] = {
        "created_at": time.time(),
        "last_activity": time.time(),
    }

A cleanup method exists:

def _cleanup_sessions(self) -> None:
    now = time.time()
    expired = [sid for sid, data in self._sessions.items()
               if now - data["last_activity"] > self.session_ttl]
    for sid in expired:
        del self._sessions[sid]

but grep across the package shows it has no call sites: it is never invoked on a timer, on request handling, or from any background task. self.session_ttl (default 3600) is stored and otherwise unused. There is no maximum-session check anywhere on the write path. As a result self._sessions grows monotonically for the lifetime of the process.

initialize is unauthenticated: in mcp_post the API-key check is skipped when no key is configured (the default), and initialize does not require a prior session. The Origin check is the only gate, and a request with no Origin header is allowed; additionally the Origin allowlist is bypassable (see the companion report on the startswith Origin-validation bypass), so the endpoint is reachable from a malicious web page as well as directly.

The server-side cancellation set in server.py has the same defect:

if method == "notifications/cancelled":
    request_id = params.get("requestId")
    if request_id:
        self._cancelled_requests.add(str(request_id))   # never cleared

self._cancelled_requests is an unbounded set that is added to but never pruned.

PoC

scripts/poc_mcp_session_dos.sh. Start the server (default config, no API key):

praisonai mcp serve --transport http-stream --host 127.0.0.1 --port 8080

Send repeated initialize requests and watch the active session count grow:

for i in $(seq 1 200); do
  curl -s -o /dev/null -X POST http://127.0.0.1:8080/mcp \
    -H 'Content-Type: application/json' -H 'Origin: http://localhost' \
    -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"x","version":"1"}}}'
done
curl -s http://127.0.0.1:8080/health

Observed on 4.6.52 after 200 requests:

{"status":"healthy","server":"praisonai","version":"1.0.0","protocol_version":"2025-11-25","active_sessions":200}

The count rises by one per request and never decreases; there is no TTL expiry and no cap. Sustained requests grow the process resident set without bound. Each session also retains any SSE event history keyed by session id, amplifying the per-session footprint.

Impact

An unauthenticated client can exhaust the memory of the host running the MCP server, leading to denial of service (the process is terminated by the OOM killer, taking down the agent endpoint). When the server is bound to a routable interface (for example --host 0.0.0.0, common in containers), this is a direct remote unauthenticated DoS. With the default localhost bind, it is reachable from any web page the operator visits, because initialize is unauthenticated and the Origin gate is bypassable. The defect is a missing cleanup wiring plus the absence of any session cap, so it manifests even under benign long-running use.

Remediation

Enforce the session TTL and cap the number of concurrent sessions: call _cleanup_sessions periodically (a background asyncio task, or opportunistically on each request) and reject new sessions with a 429/503 once a configurable maximum is reached. Bound _cancelled_requests similarly (for example an LRU or a periodic prune keyed by age), since it is also never cleared. Require authentication by default on the HTTP-stream transport so that anonymous clients cannot create sessions at all.