---
id: CVE-2026-48802
title: >-
  python-engineio is a Python implementation of the Engine.IO realtime client
  and server
summary: >-
  python-engineio is a Python implementation of the Engine.IO realtime client
  and server. Prior to version 4.13.2, an attacker can cause the creation of
  unnecessary background threads in the python-engineio server by exploiting the
  heartbe…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-770
vendor: python-engineio
product: python-engineio
affected:
  - python-engineio <= 4.13.1
patched:
  - python-engineio 4.13.2
published: '2026-08-11'
updated: '2026-09-18'
sourceUpdated: '2026-09-18T20:09:01.757'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-48802'
references:
  - url: >-
      https://github.com/miguelgrinberg/python-engineio/security/advisories/GHSA-cgwc-pv48-fhj5
    label: security-advisories@github.com
  - url: >-
      https://github.com/pypa/advisory-database/tree/main/vulns/python-engineio/PYSEC-2026-3032.yaml
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-cgwc-pv48-fhj5'
tags:
  - nvd
  - ghsa
  - pip
epss: 0.00318
epssPercentile: 0.24971
ecosystem: pip
ingestedAt: '2026-06-29T13:24:35.264Z'
---

## Overview

python-engineio is a Python implementation of the Engine.IO realtime client and server. Prior to version 4.13.2, an attacker can cause the creation of unnecessary background threads in the python-engineio server by exploiting the heartbeat mechanism, which launches a thread when a new connection is received, and when the client sends a PONG packet. This issue primarily affects synchronous servers. Asynchronous servers allocate background tasks instead of physical threads, which are lightweight and less likely to cause denial of service. However, the fix that was implemented was also applied to the asynchronous case. Version 4.13.2 addresses this issue as follows: The initial background thread (or async task( for heartbeat management is only launched if a client passes authentication in the `connect` handler; and the server now ensures that there is only one background heatbeat thread (or async task) per client at a given point in time. Out of sequence PONG packets are now discarded when an active heartbeat thread is already running.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-48802)

Affected packages:

- `python-engineio <= 4.13.1`

Patched in:

- `python-engineio 4.13.2`

Source: https://github.com/advisories/GHSA-cgwc-pv48-fhj5