Host-Only Cookie Handling Flaw in AIOHTTP

Compliance Impact

This vulnerability causes host-only cookies saved and later restored to lose their host-only status, potentially allowing cookies to be sent to unintended subdomains.

Such unintended cookie leakage could increase the risk of unauthorized data exposure or tracking, which may impact compliance with privacy regulations like GDPR or HIPAA that require strict control over personal data and user privacy.

However, the vulnerability has a low severity rating and is fixed in aiohttp version 3.14.1.

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Impact Analysis

This vulnerability can cause host-only cookies to be sent to unintended subdomains after being saved and restored, potentially exposing sensitive session or authentication information to domains that should not have access.

Such unintended cookie sharing can increase the risk of session hijacking or cross-site request forgery attacks if malicious subdomains exist or are compromised.

However, the severity of this vulnerability is rated as low.

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Executive Summary

This vulnerability occurs in the aiohttp library's CookieJar class, where host-only cookies that are saved using CookieJar.save() and later restored with CookieJar.load() lose their host-only status.

As a result, cookies that should only be sent to a specific host may instead be sent to subdomains, which can lead to unintended cookie leakage.

The issue affects aiohttp versions up to and including 3.14.0 and was fixed in version 3.14.1 by preserving the host-only flag and expiration deadlines during the save/load process.

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Detection Guidance

This vulnerability involves host-only cookies losing their host-only status when saved and restored using aiohttp's CookieJar.save() and CookieJar.load() methods. Detection would involve inspecting cookie behavior in your aiohttp-based applications to see if cookies intended to be host-only are being sent to unintended subdomains.

Since the issue is specific to the handling of cookies within the aiohttp library, there are no direct network commands to detect it. Instead, you can check the version of aiohttp in your environment to see if it is vulnerable (versions up to and including 3.14.0).

To check the aiohttp version installed, you can run the following command in your Python environment:

• python -c "import aiohttp; print(aiohttp.__version__)"

If you want to inspect cookie files saved by CookieJar.save(), you can manually check if cookies that should be host-only are missing the host-only flag or are scoped incorrectly after loading.

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Mitigation Strategies

The primary mitigation step is to upgrade the aiohttp library to version 3.14.1 or later, where this vulnerability has been fixed.

This update ensures that host-only cookies retain their host-only status when saved and restored, preventing cookies from being sent to unintended subdomains.

If upgrading immediately is not possible, consider reviewing your use of CookieJar.save() and CookieJar.load() to avoid relying on saved cookies that may have lost their host-only status.

Additionally, validate cookies after loading to ensure they conform to expected scopes and discard any that appear to be incorrectly scoped.

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