# CVE-2026-48809: python-engineio denial of service via unchecked payload size

Source: https://junglewise.ai/threats/cve-2026-48809-python-engineio-denial-of-service-via-unchecked-payload-size  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-11. Updated: 2026-06-26  
License: CC BY 4.0 with a link back

CVE-2026-48809 · Severity: high · CVSS 7.5 · Published 2026-08-11

A vulnerability in the python-engineio library, which handles real-time communication for web applications, could allow an attacker to crash the server. By sending specially crafted large messages, an attacker can force the server to consume excessive memory, leading to a denial of service. This affects applications using specific configurations like ASGI long polling or Aiohttp WebSockets.

Technologies: [python-engineio (PyPI)](https://junglewise.ai/threats/technologies/python-engineio). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-48809 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-48809 being exploited in the wild.

**How severe is CVE-2026-48809?** High severity, with a CVSS score of 7.5, published 11 August 2026.

**Which products and versions are affected?** python-engineio (PyPI) <= 4.13.1, ECOSYSTEM:introduced=0,fixed=4.13.2.

**Is there a fix for CVE-2026-48809?** Yes. python-engineio (PyPI): upgrade to 4.13.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-48809 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-48809?** Check whether you run python-engineio (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- python-engineio (PyPI): upgrade to 4.13.2 or later

  ```sh
  pip install "python-engineio>=4.13.2"
  ```


## Technical details

A resource exhaustion vulnerability (CWE-770) exists in python-engineio where incoming message sizes are not validated before being loaded into memory. This occurs in two specific scenarios: POST requests using the ASGI long polling transport, and WebSocket messages using the Aiohttp transport. A remote, unauthenticated attacker can exploit this by sending payloads exceeding intended limits, leading to a Denial of Service (DoS) via memory exhaustion. The issue is addressed in version 4.13.2 by implementing size checks before memory allocation in ASGI and leveraging Aiohttp's native WebSocket payload limits.

## Affected products

- miguelgrinberg python-engineio <= 4.13.1

## Identifiers

- CVE-2026-48809
- GHSA-m9gh-vj53-gvh9
- PYSEC-2026-3033

## Timeline

- 2026-05-23: disclosed
- 2026-06-26: advisory: GitHub Advisory published/reviewed
- 2026-06-26: patched: Version 4.13.2 released

## References

- [https://github.com/miguelgrinberg/python-engineio/security/advisories/GHSA-m9gh-vj53-gvh9](https://github.com/miguelgrinberg/python-engineio/security/advisories/GHSA-m9gh-vj53-gvh9)
- [https://api.github.com/repos/miguelgrinberg/python-engineio/security-advisories/GHSA-m9gh-vj53-gvh9](https://api.github.com/repos/miguelgrinberg/python-engineio/security-advisories/GHSA-m9gh-vj53-gvh9)

## Related threats

- [python-engineio denial of service via unbound thread allocation](https://junglewise.ai/threats/cve-2026-48802-python-engineio-denial-of-service-via-unbound-thread-allocation)
- [python-engineio vulnerable to Cross-Site Request Forgery (CSRF)](https://junglewise.ai/threats/cve-2019-13611-python-engineio-vulnerable-to-cross-site-request-forgery-csrf)