Executive brief
AIOHTTP is a popular Python library used by developers to build web servers and clients. A flaw in how it handles saved login or session information (cookies) means that certain security restrictions are lost when the application is restarted. This could allow sensitive session data intended for a specific website to be accidentally sent to its subdomains, potentially leading to unauthorized access if those subdomains are untrusted.
Technical details
A vulnerability exists in the CookieJar component of aiohttp where cookies saved via CookieJar.save() and restored via CookieJar.load() lose their host-only attribute. By default, cookies without a 'Domain' attribute should only be sent to the exact host that issued them; however, this bug causes reloaded cookies to be treated as domain cookies, making them available to all subdomains. An attacker who controls a subdomain could potentially receive sensitive cookies intended only for the parent domain. This issue is fixed in version 3.14.1, which also ensures absolute expiration deadlines are persisted and improves cookie acceptance rules during loading.
Affected products
- aio-libs aiohttp <= 3.14.0
Timeline
- 2026-06-07: patched: Fix committed to repository
- 2026-06-08: advisory: GitHub Security Advisory published
- 2026-06-22: disclosed: NVD publication date