CURL-CVE-2026-82209: domain-scoped PSL domain cookie
When libpsl support is enabled, libcurl fails to enforce the Public Suffix List boundary check when processing a Set-Cookie header where the Domain attribute explicitly matches an origin host that is itself a public suffix (e.g., Domain=co.uk set by co.uk).
Instead of coercing it into a strict host-only cookie, libcurl saves the cookie with wildcard domain scope (.co.uk). Consequently, the cookie is inappropriately included in subsequent outbound requests or HTTP redirects to arbitrary sibling subdomains under the same public suffix (e.g., attacker.co.uk).
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this behavior?
Deployments using libcurl with libpsl support enabled are affected when they process a Set-Cookie header whose Domain attribute matches an origin host that is itself a public suffix, such as co.uk.
What must an attacker be able to do to exploit it?
An attacker needs to cause libcurl to accept a cookie from a public-suffix origin with a matching Domain attribute. The resulting wildcard-scoped cookie can then be sent on later requests or redirects to sibling subdomains under that public suffix.
How can I determine whether a cookie has been affected?
Inspect cookies saved after responses from public-suffix hosts. An affected cookie is stored with wildcard domain scope, such as .co.uk, rather than being restricted as a host-only cookie for the origin host.