Guzzle: Cookie Disclosure and Injection via IP-Address Domains

Impact

CookieJar does not restrict a cookie scoped to an IP address to the exact host that set it. When a stored cookie's Domain attribute is an IPv4 literal (Domain=192.168.0.1), a bracketed IPv6 literal (Domain=[::1]), or a bare numeric value that denotes an IPv4 address (Domain=1, which is 0.0.0.1), SetCookie::matchesDomain() applies ordinary subdomain (suffix) matching to it instead of requiring an exact host. The IP-address check inside matchesDomain() is applied only to the request host and never to the cookie's own domain, and response cookies that carry an explicit Domain attribute are stored as suffix-matchable. As a result Guzzle sends such a cookie to any host whose name ends in that value as a trailing label, for example sending a Domain=192.168.0.1 cookie to evil.192.168.0.1, or a Domain=1 cookie to evil.1. The same flaw lets a look-alike host store a cookie that Guzzle then sends to the bare IP address. Depending on how the receiving service interprets the cookie, the impact is cross-host cookie disclosure, cookie injection, or session fixation.

You are affected if your application uses Guzzle's cookie support, for example new Client(['cookies' => true]) or an explicit CookieJar, reuses one cookie jar across more than one host or trust boundary, and that jar can hold a cookie scoped to an IP-address or bare-numeric host. To actually leak a cookie the application must also resolve and connect to a look-alike host whose name ends in the IP-address label, such as evil.192.168.0.1. Such names are not publicly registrable, so in practice an attacker needs some influence over name resolution, which is realistic on private, split-horizon, container, or development networks. You are not affected if you do not use Guzzle's cookie support, if you use a separate cookie jar per host or trust boundary, or if your jars never hold cookies scoped to IP-address or bare-numeric hosts. This issue is independent of public suffix list validation. Per RFC 6265, an IP-address cookie domain must match only the exact host that set it and must never match a subdomain.

Patches

The issue is patched in 7.12.3 and later. Starting in that release, Guzzle matches an IPv4 literal, a bracketed IPv6 literal, or a bare-numeric cookie Domain only against the exact request host, and no longer applies subdomain suffix matching to them.

Workarounds

If you cannot upgrade immediately, do not reuse one CookieJar instance across untrusted and trusted origins. Use a separate cookie jar per host or trust boundary, or disable cookie handling for requests to untrusted hosts, and avoid scoping cookies to IP-address or bare-numeric hosts. In particular, avoid new Client(['cookies' => true]) for any client that may contact unrelated hosts at different trust levels, because that option creates a single shared jar for the whole client.

References

• https://datatracker.ietf.org/doc/html/rfc6265#section-5.1.3
• https://datatracker.ietf.org/doc/html/rfc6265#section-5.3
• https://url.spec.whatwg.org/#concept-ipv4-parser