Cookie Security
Cookie attributes
Ultimate
cookie:
Secure attribute
The Secure
attribute indicates that the cookie is sent to a server only when a request is made with the https:
scheme (except on localhost). It only protects the confidentiality of a cookie against MitM attackers - there is no integrity protection. Therefore, cookies with this attribute can still be modified either with access to the client's hard disk or from JavaScript.
Insecure sites http:
can't set cookies with the Secure
attribute (since Chrome 52 and Firefox 52). For Firefox, the https:
requirements are ignored when the Secure
attribute is set by localhost (since Firefox 75).
HttpOnly attribute
Cookies marked with the HttpOnly
attribute are not accessible from JavaScript. The HttpOnly
attribute only protects the confidentiality of a cookie. HttpOnly
cookies can be replaced by overflowing the cookie jar from JavaScript.
Path attribute
The Path
attribute indicates the path that must exist in the requested URL for the browser to send the Cookie header. It can be used to prevent unauthorized access to cookies from other applications on the same host.
The forward slash /
character is interpreted as a directory separator, and subdirectories are matched as well. For example, for Path=/docs
:
The request paths
/docs
,/docs/
,/docs/Web/
, and/docs/Web/HTTP
will all match.The request paths
/
,/docsets
,/fr/docs
will not match.
Cookie scope vs Same-Origin Policy
Isolation two different applications on shared host
Domain attribute
The Domain
attribute defines the host to which the cookie will be sent.
If the
Domain
attribute unspecified, it defaults to the host of the current document location, excluding subdomainsIE will always send to subdomains regardless
If the
Domain
attribute is specified, cookies will be sent to that domain and all its subdomains
Expires attribute
The Expires
attribute indicates the maximum lifetime of the cookie as an HTTP-date timestamp.
If the
Expires
attribute unspecified, cookie lifetime is equal to session lifetimeIt is up to the browser to decide when the session ends
Non-persistent
session cookies may actually be persisted to survive browser restart
References:
Max-Age attribute
The Max-Age
attribute indicates the number of seconds until the cookie expires. If both Expires
and Max-Age
are set, Max-Age
has precedence.
SameSite
The SameSite
attribute prevents the browser from sending cookies along with cross-site requests. The SameSite
attribute can have one of two values (case-insensitive):
Strict
, means that the browser sends the cookie only for same-site requests, that is, requests originating from the same site that set the cookie. If a request originates from a URL different from the current one, no cookies with theSameSite=Strict
attribute are sent.Lax
, means that the cookie is not sent on cross-site requests, such as on requests to load images or frames, but is sent when a user is navigating to the origin site from an external site usingsafe
HTTP methods (for example, when following a link). This is the default behavior if the SameSite attribute is not specified. Thesafe
methods:GET, HEAD, OPTIONS
andTRACE
.None
, means that the browser sends the cookie with both cross-site and same-site requests. TheSecure
attribute must also be set when setting this value, like soSameSite=None; Secure
.
The cookies without the SameSite
in Chrome are still treated as None
during the first 2 minutes and then as Lax
, check out Bypass SameSite Cookies Default to Lax and get CSRF
Keep in mind that same-site and cross-site requests are not the same thing. The SameSite cookie attribute is only concerned with cross-site requests. It does not affect cross-origin requests that refer to the same-site, check out The great SameSite confusion
References:
Cookie prefix
The cookie prefix allows you to pass metadata about a cookie and notify a client that certain attributes have been set. The following prefixes are supported:
__Secure-
tells the browser that theSecure
attribute is required.__Host-
tells the browser that thePath=/
andSecure
attributes are required, and at the same time that theDomain
attribute should not be present (and therefore, can not be sent to subdomains).
References:
Cookie-list sorting
The RFC6265 standard defines the order of cookies:
Therefore, if a vulnerable application uses the first cookie, you can force it to use your cookie by adding the Path
attribute with a longer path.
References
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