Origin validation error in aiohttp - #VU153860
Published: October 7, 2026
Vulnerability identifier: #VU153860
CSH Severity: Low
CVSS v4: 4.6 [CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-346
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to remove host-only protections from an existing parent-domain cookie.
The vulnerability exists due to improper enforcement of cookie origin restrictions in aiohttp cookie handling when processing cookies from a subdomain. A remote attacker can supply a cookie from an untrusted subdomain to remove host-only protections from an existing parent-domain cookie.
Exploitation requires a user to access the untrusted subdomain. Most use cases do not reflect these cookies to a browser, limiting the practical impact.
Affected software
aiohttp
Remediation
Install security update from vendor's website.
aiohttp - update to 3.14.4