# CVE-2026-48802: python-engineio has unbound thread allocation that can cause denial of service

> An attacker can cause denial of service in python-engineio synchronous servers by triggering unbound thread allocation via the heartbeat mechanism.

- **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:** 13 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-48802, GHSA-cgwc-pv48-fhj5, PYSEC-2026-3032, ROOT-APP-PYPI-CVE-2026-48802, UBUNTU-CVE-2026-48802

## What is CVE-2026-48802?

CVE-2026-48802 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. 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.

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

## Which versions are affected by CVE-2026-48802?

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 |

## How do I fix CVE-2026-48802?

Upgrade python-engineio to 4.13.2 or later.

## Is CVE-2026-48802 being exploited?

There is no known exploitation of CVE-2026-48802 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-48802 and fix it if it is affected.

What it is: CVE-2026-48802 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-2026-48802 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-2026-48802/ (Markdown: https://insights.sbomify.com/CVE-2026-48802/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-48802
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-48802
- OSV: https://osv.dev/vulnerability/CVE-2026-48802

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-48802/
Summaries are generated and may contain mistakes; the official description above is the record.