# CVE-2026-111749: aiohttp host-only cookie scope bypass in subdomain handling

Source: https://junglewise.ai/threats/cve-2026-111749-aiohttp-is-an-asynchronous-http-client-server-framework-for  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-19. Updated: 2026-10-19  
License: CC BY 4.0 with a link back

CVE-2026-111749 · Severity: medium · CVSS 4 · Published 2026-10-19

aiohttp is an HTTP client/server framework for Python. A subdomain can strip the host-only protection flag from cookies belonging to a parent domain, allowing broader cookie scope than intended. This affects applications that reflect such cookies to browsers, potentially exposing session data or other sensitive cookie content.

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

## Quick answers

**Is CVE-2026-111749 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-111749 being exploited in the wild.

**How severe is CVE-2026-111749?** Medium severity, with a CVSS score of 4, published 19 October 2026.

**Which products and versions are affected?** Aio-Libs Aiohttp before 3.14.4; aiohttp (PyPI) <= 3.14.3, ECOSYSTEM:introduced=0,fixed=3.14.4.

**Is there a fix for CVE-2026-111749?** Yes. aiohttp (PyPI): upgrade to 3.14.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-111749 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-111749?** Check whether you run Aio-Libs 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 3.14.4 or later

  ```sh
  pip install "aiohttp>=3.14.4"
  ```


## Technical details

The vulnerability allows a subdomain to remove the host-only scope flag from an existing parent-domain cookie via cookie expiration or replacement handling. An attacker who can direct a user to visit an untrusted subdomain can exploit this to change cookie scope, though the impact is limited when applications do not reflect those cookies back to a browser or rely on host-only protection.

## Affected products

- aio-libs aiohttp before 3.14.4

## Identifiers

- CVE-2026-111749
- GHSA-gx76-c99x-2c96

## Timeline

- 2026-10-19: disclosed

## References

- [https://github.com/aio-libs/aiohttp/commit/6a07c171ef9f3be583e2907dcd1931372efca8d6](https://github.com/aio-libs/aiohttp/commit/6a07c171ef9f3be583e2907dcd1931372efca8d6)
- [https://github.com/aio-libs/aiohttp/releases/tag/v3.14.4](https://github.com/aio-libs/aiohttp/releases/tag/v3.14.4)

## Related threats

- [AIOHTTP WebSocket memory exhaustion via fragmented frames](https://junglewise.ai/threats/cve-2026-123817-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [aiohttp HTTP request smuggling in pure Python parser](https://junglewise.ai/threats/cve-2026-111750-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [aiohttp Request scheme manipulation in absolute-form requests](https://junglewise.ai/threats/cve-2026-111748-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [AIOHTTP multipart request file descriptor exhaustion](https://junglewise.ai/threats/cve-2026-111066-aiohttp-is-an-asynchronous-http-client-server-framework-for)
- [aiohttp cookie Max-Age integer overflow causes connection pool exhaustion](https://junglewise.ai/threats/cve-2026-111065-aiohttp-is-an-asynchronous-http-client-server-framework-for)