# CVE-2026-34514: aiohttp CRLF injection in multipart content type header

Source: https://junglewise.ai/threats/cve-2026-34514-aiohttp-crlf-injection-in-multipart-content-type-header  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-01. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-34514 · Severity: medium · CVSS 5.3 · Published 2026-04-01

aiohttp is a popular Python HTTP client library used by many web applications. A CRLF injection vulnerability in the multipart request construction allows an attacker who can control the content_type parameter to inject additional HTTP headers or manipulate the request structure, potentially leading to request smuggling or header spoofing attacks.

Technologies: [Aiohttp](https://junglewise.ai/threats/technologies/aiohttp-aiohttp), [aiohttp (PyPI)](https://junglewise.ai/threats/technologies/aiohttp). Vendors: [Aiohttp](https://junglewise.ai/threats/vendors/aiohttp), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-34514 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34514 being exploited in the wild.

**How severe is CVE-2026-34514?** Medium severity, with a CVSS score of 5.3, published 1 April 2026.

**Which products and versions are affected?** aiohttp (PyPI) ECOSYSTEM:introduced=0,fixed=3.13.4.

**Is there a fix for CVE-2026-34514?** Yes. aiohttp (PyPI): upgrade to 3.13.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-34514 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-34514?** Check whether you run Aiohttp or aiohttp (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- aiohttp (PyPI): upgrade to 3.13.4 or later

  ```sh
  pip install "aiohttp>=3.13.4"
  ```


## Technical details

This vulnerability is a CRLF (Carriage Return Line Feed) injection in the multipart part content type header construction. The root cause is insufficient validation of user-supplied content_type parameters when building multipart request bodies. An attacker who can control this parameter can inject carriage return and line feed characters to break out of the header and inject arbitrary headers or content. The attack requires that an application passes untrusted data directly to the multipart content_type parameter. Exploitation could result in request smuggling or header injection attacks. A patch was released in version 3.13.4 (commit 9a6ada97e2c6cf1ce31727c6c9fcea17c21f6f06).

## Affected products

- aio-libs aiohttp before 3.13.4

## Identifiers

- CVE-2026-34514
- GHSA-2vrm-gr82-f7m5
- PYSEC-2026-2096

## Timeline

- 2026-04-01: disclosed: Advisory published on GitHub
- 2026-04-01: patched: Fix released in version 3.13.4

## References

- [https://github.com/aio-libs/aiohttp/security/advisories/GHSA-2vrm-gr82-f7m5](https://github.com/aio-libs/aiohttp/security/advisories/GHSA-2vrm-gr82-f7m5)

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