# CVE-2026-48809: python-engineio has possible denial of service due to maximum payload size sometimes not being enforced

> Attackers can cause denial of service via memory exhaustion in specific ASGI or Aiohttp configurations by sending oversized payloads that bypass size checks.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Aug 2026
- **Updated:** 11 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-48809, GHSA-m9gh-vj53-gvh9, PYSEC-2026-3033, ROOT-APP-PYPI-CVE-2026-48809, UBUNTU-CVE-2026-48809, openSUSE-SU-2026:11170-1

## What is CVE-2026-48809?

CVE-2026-48809 is a high-severity denial of service vulnerability in miguelgrinberg python-engineio, published on 11 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

python-engineio is a Python implementation of the Engine.IO realtime client and server. Versions prior to 4.13.2 have two specific configurations of the python-engineio server in which the size of incoming messages is not checked before the messages are loaded into memory. An attacker can take advantage of these to cause unnecessary memory allocations in the python-engineio server. The two cases are POST requests, when using ASGI with the long polling transport and WebSocket messages, when using Aiohttp with the WebSocket transport. Version 4.13.2 addresses this issue. ASGI severs now only load the body of incoming requests into memory after the client is confirmed to be known and authenticated, and the payload size is below the maximum allowed size. Requests that do not comply with these requirements are discarded. Aiohttp servers configure the maximum payload size in the underlying WebSocket layer from Aiohttp, so that large messages are discarded by Aiohttp before they are delivered to python-engineio.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling)

## Which versions are affected by CVE-2026-48809?

3 open source packages ship an affected version, including python-engineio.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `python-engineio` | PyPI | All versions | 4.13.2 |
| `python-engineio` | PyPI | All versions | 4.13.2 |
| `python-engineio` | PyPI | All versions | 4.13.2 |
| `python-python-engineio` | openSUSE:Tumbleweed | All versions | 4.13.3-1.1 |

## How do I fix CVE-2026-48809?

Upgrade python-engineio to 4.13.2 or later.

## Is CVE-2026-48809 being exploited?

There is no known exploitation of CVE-2026-48809 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48809 and fix it if it is affected.

What it is: CVE-2026-48809 is a high-severity denial of service vulnerability in miguelgrinberg python-engineio, published on 11 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-48809 in the wild and no public exploit code.

Affected packages and fixed versions:
- python-engineio (PyPI): affected all versions; fixed in 4.13.2
- python-engineio (PyPI): affected all versions; fixed in 4.13.2
- python-engineio (PyPI): affected all versions; fixed in 4.13.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-48809/ (Markdown: https://insights.sbomify.com/CVE-2026-48809/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48809
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48809
- OSV: https://osv.dev/vulnerability/CVE-2026-48809

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-48809/
Summaries are generated and may contain mistakes; the official description above is the record.