AIOHTTP: Cookie from subdomain can remove Host-Only Scope from existing cookies

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

2.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-111749: 0.38% estimated exploitation activity in the next 30 days; percentile 32.50 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A subdomain can remove the Host-Only flag from an existing cookie to a parent domain. Impact A user accessing untrusted subdomains could see their Host-Only protections stripped from cookies. Given most usecases won't reflect these cookies to a browser, the impact is limited.

Published by the source

20 Oct 2026, 19:58 UTC

Last modified by the source

20 Oct 2026, 20:15 UTC

Source last checked

26 Oct 2026, 13:55 UTC

1. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-gx76-c99x-2c96

2. Revision 3 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-gx76-c99x-2c96

4. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-gx76-c99x-2c96

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-111749

Advisory: AIOHTTP: Cookie from subdomain can remove Host-Only Scope from existing cookies
IDs: CVE-2026-111749, GHSA-gx76-c99x-2c96
Record: https://patchnext.com/advisories/cve-2026-111749 (revision 4, source checked 26 Oct 2026, 13:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: aiohttp 3.14.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI aiohttp: affected <= 3.14.3; fixed in 3.14.4

## Suggested inspection (read-only)
- `python -m pip show aiohttp`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on aiohttp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-gx76-c99x-2c96 (GitHub-reviewed advisory GHSA-gx76-c99x-2c96 lists affected ranges: PyPI aiohttp >=0 <=3.14.3)
- Verified: https://osv.dev/vulnerability/GHSA-gx76-c99x-2c96 (OSV record GHSA-gx76-c99x-2c96 lists affected ranges: PyPI aiohttp >=0 <3.14.4 (fixed))

Commands are suggestions: review each one before running it.