# CVE-2026-123817: AIOHTTP WebSocket frame reassembly permits excessive memory consumption from tiny reads


- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 9 Nov 2026
- **Updated:** 9 Nov 2026
- **Also known as:** CLEANSTART-2026-JF82982, CLEANSTART-2026-NK38254, DEBIAN-CVE-2026-123817, ECHO-e2f8-166f-a041, GHSA-2g87-pp6c-29x5, MINI-547f-39hj-v7jj, MINI-cp36-5rqf-f24q, MINI-jg9v-pxfh-77r9, ROOT-APP-PYPI-CVE-2026-123817, ROOT-APP-PYPI-GHSA-2g87-pp6c-29x5, UBUNTU-CVE-2026-123817

## What is CVE-2026-123817?

CVE-2026-123817 is a high-severity vulnerability in aio-libs aiohttp, published on 9 Nov 2026. 

### Official description

AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, the WebSocket reader retains one bytes object for each transport read while reassembling an incomplete frame. A malicious peer can split a frame into many tiny reads so per-object overhead substantially exceeds the payload bytes allowed by max_msg_size. The condition affects a server receiving frames from a malicious client and a client receiving frames from a malicious server, and can cause excessive memory consumption or denial of service. This issue is fixed in version 3.14.4.

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

## Which versions are affected by CVE-2026-123817?

1 open source package ship an affected version, including aiohttp.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `aiohttp` | PyPI | All versions | 3.14.4 |

## How do I fix CVE-2026-123817?

Upgrade aiohttp to 3.14.4 or later.

## Is CVE-2026-123817 being exploited?

There is no known exploitation of CVE-2026-123817 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123817 and fix it if it is affected.

What it is: CVE-2026-123817 is a high-severity vulnerability in aio-libs aiohttp, published on 9 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-123817 in the wild and no public exploit code.

Affected packages and fixed versions:
- aiohttp (PyPI): affected all versions; fixed in 3.14.4

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-2026-123817/ (Markdown: https://insights.sbomify.com/CVE-2026-123817/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123817
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123817
- OSV: https://osv.dev/vulnerability/CVE-2026-123817

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-123817/
Summaries are generated and may contain mistakes; the official description above is the record.