# AIOHTTP is vulnerable to HTTP Request/Response Smuggling through incorrect parsing of chunked trailer sections

Advisory record · `GHSA-9548-qrrj-x5pj`

- **Identifiers:** `GHSA-9548-qrrj-x5pj` · `CVE-2025-53643` · `PYSEC-2026-1104`
- **State:** Confirmed
- **Severity:** CVSS 1.7 Low
- **Critical:** No
- **Weakness (CWE):** [CWE-444](https://cwe.mitre.org/data/definitions/444.html)
- **Tags:** [HTTP request smuggling](https://agentprime.io/advisories/tag/request-smuggling.md)
- **Published:** 14 Jul 2025
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 14 Jul 2025, 19:33 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `aiohttp` (PyPI): affected `<3.12.14`; fixed in `3.12.14`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Affected: aiohttp versions before 3.12.14. The pure Python HTTP parser does not parse trailer sections of chunked requests, which enables request smuggling. This applies only when aiohttp runs without its C extensions or with AIOHTTP_NO_EXTENSIONS enabled. An attacker could use smuggling to bypass firewall or proxy protections. Upgrade to aiohttp 3.12.14 or later.

Written 5 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 1.7 Low, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0036, the 29th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:34 UTC: First seen by agentprime
- 31 Oct 2026, 14:34 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-9548-qrrj-x5pj)

## Sources

- [GitHub Advisory Database: GHSA-9548-qrrj-x5pj](https://github.com/advisories/GHSA-9548-qrrj-x5pj)
- [OSV: GHSA-9548-qrrj-x5pj](https://osv.dev/vulnerability/GHSA-9548-qrrj-x5pj)
- <https://github.com/aio-libs/aiohttp/security/advisories/GHSA-9548-qrrj-x5pj>
- <https://nvd.nist.gov/vuln/detail/CVE-2025-53643>
- <https://github.com/aio-libs/aiohttp/commit/e8d774f635dc6d1cd3174d0e38891da5de0e2b6a>
- <https://github.com/aio-libs/aiohttp>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-9548-qrrj-x5pj>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-9548-qrrj-x5pj/>. Everything for agents: <https://agentprime.io/llms.txt>.