Oblivious Proxy FeedbackAkamaiEmbassy Golf Link Business ParkBangaloreKarnataka560071Indiakondtir@gmail.comCitrix Systems, Inc.4988 Great America PkwySanta ClaraCA95054USAdanwing@gmail.comOrangeRennes35000Francemohamed.boucadair@orange.comTeam Digitale, Italian Governmentrobipolli@gmail.comohaiTo provide equitable service to clients, servers often rate-limit
incoming requests, for example, based upon the source IP address.
However, oblivious HTTP removes the ability for the server to
distinguish amongst clients so the server can only rate-limit traffic
from the oblivious proxy. This harms all clients behind that oblivious
proxy.This specification enables a server to convey rate-limit information
to an oblivious proxy, which can use it to apply rate-limit policies on
oblivious clients. Cooperating oblivious proxies can thus provide more
equitable service to their distinguishable clients without impacting on
all clients behind that oblivious proxy.Oblivious HTTP requires three parties to
exchange HTTP messages: the client, the proxy, and the target (formally,
the Oblivious Request Resource and Oblivious Target Resource). Oblivious
HTTP enables a client to send requests to a target in such a way that
the target cannot tell whether two requests came from the same client,
and the proxy cannot see the contents of the requests.Since oblivious clients are located behind a proxy, a target cannot
distinguish between well-behaving and malicious clients: an unexpected
behavior from one or more clients can then impact on all the
intermediated clients, as described in Section 8.2.1 of . This can be problematic when the target
implements rate limiting policies based on an information masked by the
intermediary, such as the source IP address.This document defines a mechanism that allows Oblivious request and
target resource to provide rate-limit information to an Oblivious proxy
via the RateLimit fields defined in .
This is useful when such servers identify traffic anomalies or
unexpected request volumes. The Oblivious proxy can then use this
information to apply rate-limit policies on oblivious clients.While provides enough information to
generic clients to shape their request policy and avoid being throttled
out, this specification allows an Oblivious request and target resource
to indicate their RateLimit information is intended for the Oblivious
proxy (rather than to the client).How an Oblivious proxy can use this information to avoid being
throttled out or shape its request policy is outside the scope of this
specification.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP 14
when, and
only when, they appear in all capitals, as shown here.The terms "content", "receiver", "request", and "response" are to be
interpreted as described in .The terms "Encapsulated request", "Encapsulated response", "Oblivious
proxy resource", "Oblivious request resource", "Oblivious target
resource", and "Client" are to be interpreted as described in .The collective term "Oblivious resource" indicates either an
"Oblivious request resource" or an "Oblivious target resource".The terms "quota policy", "service limit", "expiring limit", and
"RateLimit fields" are to be interpreted as described in .This document uses the Integer type from .An Oblivious resource that uses RateLimit fields to return service limit information MAY add
the "ohttp-target" quota policy parameter defined in to signal to the receiver that the associated
quota policy is intended for an Oblivious proxy. For example, when an
Oblivious target identifies a high frequency or high volume anomalies in
the HTTP requests it would include the "ohttp-target" parameter.The term "Oblivious Proxy Feedback" denotes both the mechanism
described in this specification and the complete set of RateLimit fields
together with the "ohttp-target" parameter.To know whether the RateLimit fields provides Oblivious Proxy
Feedback (see Section 3.1), an Oblivious proxy MUST: Identify the quota policy associated to the expiring limit.Check whether the "ohttp-target" parameter is present and its
syntax is correct.In the example shown in , the expiring
limit value is "100", so the associated quota policy is the second one.
This quota policy includes the "ohttp-target" parameter: this indicates
that the RateLimit fields are intended for an Oblivious proxy.The following quota policy parameter is defined for the
RateLimit-Limit field :Indicates that the associated quota
policy provides Oblivious Proxy Feedback. This parameter is
OPTIONAL.The "ohttp-target" parameter has the following syntax:Its value MUST be an Integer (Section 3.3.1 of ) and indicates whether the quota
policy is applicable to all the clients that are serviced by the
Oblivious proxy or applicable only to a specific client. The
"ohttp-target" parameter MUST have one of the following values:Indicates that RateLimit fields are applicable to
all the clients that are serviced by the same Oblivious proxy.Indicates that RateLimit fields are applicable
only to the offending client. For example, this value is used if
the client is attacking the server (e.g., the client is using an
abnormal header that matches an attack pattern). The Oblivious
proxy can shadowban requests from the offending client for a
certain duration instead of rate-limiting the requests when the
client has a high ratio of malicious requests to legitimate
requests. Other values MUST cause the parameter to be ignored.The "ohttp-target" parameter MUST NOT appear more than once in a
quota policy. If the parameter is malformed or its value is invalid,
it MUST be ignored, and the receiving Oblivious proxy MUST NOT attempt
to fix neither the parameter nor its value. That is, the RateLimit
fields must not be considered as providing Oblivious Proxy
Feedback.An Oblivious proxy receiving RateLimit fields providing Oblivious
Proxy Feedback will do the following:It MUST remove the RateLimit fields from the response, since
they are not intended to be forwarded to clients.It MAY add a new set of RateLimit fields that are intended to
be forwarded to a client.An Oblivious request resource receiving RateLimit fields providing
Oblivious Proxy Feedback will do the following:It MUST remove the RateLimit fields from the HTTP response,
since they are not intended to be forwarded to the client. It,
then, encapsulates the HTTP response.It MUST add the above RateLimit fields to the response
containing the encapsulated response sent to the Oblivious proxy,
so that the Oblivious proxy can access them.If the RateLimit fields along with the "ohttp-target" parameter are
generated by the oblivious request resource before removing the
protection (including being unable to remove the encapsulation for any
reason)(Section 6.2 of ), it will result
in the RateLimit fields added in the response being sent without
protection in response to a POST request from a client.While this specification does not mandate specific traffic shaping
actions for Oblivious proxies in addition to the ones indicated in
, an Oblivious proxy failing to
reshape traffic from a specific client or from all the clients
according to the received Oblivious Proxy Feedback can experience
different levels of service denial by the Oblivious request and target
resources. There is no explicit mechanism for an Oblivious proxy to
indicate to the server that the rate-limit information was processed
or was ignored.The following quota policy parameter is defined for the
RateLimit-Limit field defined in :Is used by the Oblivious resource to
convey the likeliness that an Oblivious request is malicious. This
parameter is OPTIONAL.Note that sf-string is defined in Section 3.3.3 of .The value of the "attack-severity" parameter is a String (Section
3.3.3 of ) that takes one of the values
defined in . This parameter MUST NOT
appear more than once in a quota policy. If the parameter is malformed
or its value is invalid, the parameter MUST be ignored, and the proxies
MUST NOT attempt to fix neither the parameter nor the value.The example depicted in illustrates the
use of the "ohttp-target" parameter. An oblivious target resource
receives a malformed message and uses the source IP address to identify
that it was an oblivious HTTP request decapsulated by an oblivious
request resource. The Oblivious target resource generates a 400 response
and adds the RateLimit fields along with the "ohttp-target" quota policy
parameter. The oblivious request resource proceeds as follows: Copy the RateLimit fields from the original response.Remove them from the original response before encapsulating
it.Generate a single 200 response containing the encapsulated
response for the oblivious proxy resource along with the copied
RateLimit fields.The response that is generated by the Oblivious request resource is
depicted in . This response includes an
unregistered, informative "comment" quota policy parameter providing the
rationale for the "attack- severity".The security considerations for the Oblivious HTTP protocol (Section
8 of ) as well as the ones for
RateLimit-Limit fields (Section 6 of )
apply. The following sub-sections discuss security considerations
specific to this specification.While Oblivious HTTP relies upon an Oblivious proxy to prevent
leaking the client identity to the Oblivious resources, it might be
the case that the Oblivious proxy colludes with clients in attacking
Oblivious resources. RateLimit fields might disclose operational
capacity information useful to design denial of service attacks or to
circumvent defensive measures put in place by the Oblivious resources
(Section 6.2 of ). The Oblivious
target and request resources SHOULD convey Oblivious Proxy Feedback
only to trusted Oblivious proxies.Attacks against the Oblivious Request and Target Resources can be
classified into three primary categories:A client deliberately sends a malformed encapsulated request
causing decryption failure or decryption overload failure on the
oblivious request resource. This causes the oblivious request
resource to send an error status code back to the oblivious
proxy.A client deliberately sends an HTTP request that causes an HTTP
error on the oblivious target resource. This might be a malformed
HTTP request, or request for a missing resource.A botnet performing an application layer denial of service
attack (e.g. HTTP flood) against an Oblivious resource. Because
each bot in a botnet makes seemingly legitimate network requests
the traffic may appear "normal" in origin, nonetheless as a whole
it not only can saturate the Oblivious resources, but also makes
appear the Oblivious proxy as an attacker. This might be too many
requests from a single client, too many requests from the clients
behind the same oblivious proxy or too many requests from all
clients on the Internet.This specification requests IANA to add the following parameters to
the "Hypertext Transfer Protocol (HTTP) RateLimit Parameters" registry
defined in .Thanks to Lucas Pardue, Rich Salz, and Brandon Williams for the
discussion and comments.HTTP SemanticsAdobeFastlygreenbytes GmbHThe Hypertext Transfer Protocol (HTTP) is a stateless
application- level protocol for distributed, collaborative,
hypertext information systems. This document describes the overall
architecture of HTTP, establishes common terminology, and defines
aspects of the protocol that are shared by all versions. In this
definition are core protocol elements, extensibility mechanisms,
and the "http" and "https" Uniform Resource Identifier (URI)
schemes. This document updates RFC 3864 and obsoletes RFC 2818,
RFC 7231, RFC 7232, RFC 7233, RFC 7235, RFC 7538, RFC 7615, RFC
7694, and portions of RFC 7230.RateLimit Fields for HTTPTeam Digitale, Italian GovernmentRed HatThis document defines the RateLimit-Limit, RateLimit-Remaining,
RateLimit-Reset fields for HTTP, thus allowing servers to publish
current service limits and clients to shape their request policy
and avoid being throttled out.Structured Field Values for HTTPThis document describes a set of data types and associated
algorithms that are intended to make it easier and safer to define
and handle HTTP header and trailer fields, known as "Structured
Fields", "Structured Headers", or "Structured Trailers". It is
intended for use by specifications of new HTTP fields that wish to
use a common syntax that is more restrictive than traditional HTTP
field values.Oblivious HTTPMozillaCloudflareThis document describes a system for the forwarding of
encrypted HTTP messages. This allows a client to make multiple
requests of a server without the server being able to link those
requests to the client or to identify the requests as having come
from the same client.Incident Object Description Exchange Format v2
(IODEF)IANA