Privacy/Features/Shortened HTTP Referer header

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Status

Shortened HTTP Referer header
Stage	Development
Status	`
Release target	`
Health	OK
Status note	`

{{#set:Feature name=Shortened HTTP Referer header

|Feature stage=Development |Feature status=` |Feature version=` |Feature health=OK |Feature status note=` }}

Team

Product manager	Sid Stamm
Directly Responsible Individual	Sid Stamm
Lead engineer	Sid Stamm
Security lead	Curtis Koenig
Privacy lead	Sid Stamm
Localization lead	`
Accessibility lead	`
QA lead	Mihai Morar
UX lead	`
Product marketing lead	`
Operations lead	`
Additional members	Owen Chu

{{#set:Feature product manager=Sid Stamm

|Feature feature manager=Sid Stamm |Feature lead engineer=Sid Stamm |Feature security lead=Curtis Koenig |Feature privacy lead=Sid Stamm |Feature localization lead=` |Feature accessibility lead=` |Feature qa lead=Mihai Morar |Feature ux lead=` |Feature product marketing lead=` |Feature operations lead=` |Feature additional members=Owen Chu }}

Open issues/risks

• Site breakage (tolerable? need to quantify this)
• User confusion (make it hidden pref?)

Stage 1: Definition

1. Feature overview

There is the desire to remove the Referer header outright, possibly in favor of the Origin header or something with less information. It can leak sensitive data accidentally and can be abused as a form of ambient authority. Unfortunately, we can't just stop sending it on requests because too many things on the web might break. Sites like Facebook have expressed a desire for a referer-shortening capability, so this feature benefits both users and site developers.

This feature adds a way to attenuate the information that's sent as the referrer. This is multiple phases:

Phase 1: Plumbing for global and site-specific control. In the first phase, we will create a global pref so power users and addons can select at most how much of the URL is sent as referrer, globally. Additionally, on a site-by-site basis (probably via permission manager) a referrer policy can be applied to override the global setting.

Phase 2: Site-based control via CSP header and tag attributes. In the second phase, we enable sites to reduce the amount of data transmitted in referrers generated on their site. This is done by the site sending a signal with Content Security Policy response header indicating that outgoing referrers should be reduced. Stripping options should include the same options mentioned in phase 1. Sites will be able to specify a default policy for their pages, but we will also implement some per-link control (One mechanism could be to support the rel="noreferrer" attribute to omit referers from link clicks, or similar).

Phase 3: Site-based control via meta tag. Once the CSP HTTP response header can be used to set a site policy, we will extend CSP to be settable via the meta tag. This way sites can specify a referrer policy without having to send an HTTP header.

Note: Site-based control could be accomplished using the meta referrer tag, but we are opting to implement the same functionality in CSP to combine the security/privacy features. See whatwg wiki and see also bug 704320.

Phase 4: New Firefox defaults. Once sites have better control, we will decide how much to limit referrer sending by default (same-origin and cross-origin). Right now too much information is transmitted in referer headers, and we should reduce that to the extent possible. In this phase, we'll have an open discussion in dev-privacy about what defaults to choose.

Phase 5: Extra bonus phase - UI for users to control how much referrer is sent on a global basis, likely in the privacy settings for Firefox. Additionally, per-site control in the permissions and siteinfo UI. This may not be necessary if Phase 4 is successful and there's not much referrer sending by default.

See also: bug 587523

2. Users & use cases

Nice document from Dan Aurbach: https://bug822869.bugzilla.mozilla.org/attachment.cgi?id=694472

Leaking search terms

From bug 587523#c0: "An example of this can be seen by searching for 'no knead bread' with Google, and clicking on the 4th search result, which takes you to www.breadtopia.com/basic-no-knead-method/, a page which "helpfully" lets you know that it is aware of the search terms that brought you to the site."

Outbound link anonymization

Many sites like gmail send outbound links through a common redirect to strip off any information that may be present in the URL. Supporting rel="noreferrer" reduces the need for extra HTTP traffic and redirects.

3. Dependencies

`

4. Requirements

• Test plan must be created and implemented
• Use cases must be clearly outlined and it must be clear how the feature addresses each.
• Initially, Phase 1 (user-set) should not change default behavior until user initiates change.
• Default referer behavior for sites should not change until sites activate attenuation features.

Non-goals

• We are not removing the HTTP referer header
• We are not replacing the HTTP referer header
• This is not the Origin header

Stage 2: Design

5. Functional specification

See also the noreferrer link type

6. User experience design

`

Stage 3: Planning

7. Implementation plan

Phase 1:

• [DONE] global default referrer policy via pref (bug 822869)
• [ON TRACK] site-specific setting via permission (bug 966505)

Phase 2:

• [DONE] CSP referrer directive support (bug 965727)
• [DONE] noreferrer attribute for anchor tags (bug 530396)
• [NEW] referrer (policy) attribute for anchor tags

Phase 3:

• [DONE] meta tag support for CSP (bug 663570)

Phase 4:

• [NEW] discussion in dev-privacy about measuring success of new referrer defaults
• [NEW] discussion in dev-privacy to choose new policy (and measurement of its effects)
• [NEW] change global default policy for referrer bug 122453

Phase 5:

• [NEW] decide if this phase should be dropped or completed
• [NEW] about:permissions and siteInfo UI for per-site referrer settings
• [NEW] privacy settings pane UI for global referrer settings

8. Reviews

Security review

`

Privacy review

`

Localization review

`

Accessibility

`

Quality Assurance review

`

Operations review

`

Stage 4: Development

9. Implementation

See above in Planning section for progress. Just some links here.

• Facebook write-up on "HTTP-Referer" woes
• the rel="noreferrer" attribute
• bug 587523: strip referrer in a future anonymous mode

Stage 5: Release

10. Landing criteria

• Has tests
• Tests pass on B2G, Android and Desktop

{{#set:Feature open issues and risks=* Site breakage (tolerable? need to quantify this)

• User confusion (make it hidden pref?)

|Feature overview=There is the desire to remove the Referer header outright, possibly in favor of the Origin header or something with less information. It can leak sensitive data accidentally and can be abused as a form of ambient authority. Unfortunately, we can't just stop sending it on requests because too many things on the web might break. Sites like Facebook have expressed a desire for a referer-shortening capability, so this feature benefits both users and site developers.

This feature adds a way to attenuate the information that's sent as the referrer. This is multiple phases:

Phase 1: Plumbing for global and site-specific control. In the first phase, we will create a global pref so power users and addons can select at most how much of the URL is sent as referrer, globally. Additionally, on a site-by-site basis (probably via permission manager) a referrer policy can be applied to override the global setting.

Phase 2: Site-based control via CSP header and tag attributes. In the second phase, we enable sites to reduce the amount of data transmitted in referrers generated on their site. This is done by the site sending a signal with Content Security Policy response header indicating that outgoing referrers should be reduced. Stripping options should include the same options mentioned in phase 1. Sites will be able to specify a default policy for their pages, but we will also implement some per-link control (One mechanism could be to support the rel="noreferrer" attribute to omit referers from link clicks, or similar).

Phase 3: Site-based control via meta tag. Once the CSP HTTP response header can be used to set a site policy, we will extend CSP to be settable via the meta tag. This way sites can specify a referrer policy without having to send an HTTP header.

Note: Site-based control could be accomplished using the meta referrer tag, but we are opting to implement the same functionality in CSP to combine the security/privacy features. See whatwg wiki and see also bug 704320.

Phase 4: New Firefox defaults. Once sites have better control, we will decide how much to limit referrer sending by default (same-origin and cross-origin). Right now too much information is transmitted in referer headers, and we should reduce that to the extent possible. In this phase, we'll have an open discussion in dev-privacy about what defaults to choose.

Phase 5: Extra bonus phase - UI for users to control how much referrer is sent on a global basis, likely in the privacy settings for Firefox. Additionally, per-site control in the permissions and siteinfo UI. This may not be necessary if Phase 4 is successful and there's not much referrer sending by default.

See also: bug 587523 |Feature users and use cases=Nice document from Dan Aurbach: https://bug822869.bugzilla.mozilla.org/attachment.cgi?id=694472

Leaking search terms

From bug 587523#c0: "An example of this can be seen by searching for 'no knead bread' with Google, and clicking on the 4th search result, which takes you to www.breadtopia.com/basic-no-knead-method/, a page which "helpfully" lets you know that it is aware of the search terms that brought you to the site."

Outbound link anonymization

Many sites like gmail send outbound links through a common redirect to strip off any information that may be present in the URL. Supporting rel="noreferrer" reduces the need for extra HTTP traffic and redirects.

|Feature dependencies=` |Feature requirements=* Test plan must be created and implemented

• Use cases must be clearly outlined and it must be clear how the feature addresses each.
• Initially, Phase 1 (user-set) should not change default behavior until user initiates change.
• Default referer behavior for sites should not change until sites activate attenuation features.

|Feature non-goals=* We are not removing the HTTP referer header

• We are not replacing the HTTP referer header
• This is not the Origin header

|Feature functional spec=See also the noreferrer link type |Feature ux design=` |Feature implementation plan=Phase 1:

• [DONE] global default referrer policy via pref (bug 822869)
• [ON TRACK] site-specific setting via permission (bug 966505)

Phase 2:

• [DONE] CSP referrer directive support (bug 965727)
• [DONE] noreferrer attribute for anchor tags (bug 530396)
• [NEW] referrer (policy) attribute for anchor tags

Phase 3:

• [DONE] meta tag support for CSP (bug 663570)

Phase 4:

• [NEW] discussion in dev-privacy about measuring success of new referrer defaults
• [NEW] discussion in dev-privacy to choose new policy (and measurement of its effects)
• [NEW] change global default policy for referrer bug 122453

Phase 5:

• [NEW] decide if this phase should be dropped or completed
• [NEW] about:permissions and siteInfo UI for per-site referrer settings
• [NEW] privacy settings pane UI for global referrer settings

|Feature security review=` |Feature privacy review=` |Feature localization review=` |Feature accessibility review=` |Feature qa review=` |Feature operations review=` |Feature implementation notes=See above in Planning section for progress. Just some links here.

• Facebook write-up on "HTTP-Referer" woes
• the rel="noreferrer" attribute
• bug 587523: strip referrer in a future anonymous mode

|Feature landing criteria=* Has tests

• Tests pass on B2G, Android and Desktop

}}

Feature details

Priority	P1
Rank	4
Theme / Goal	Tracking Control
Roadmap	Privacy
Secondary roadmap	`
Feature list	Platform
Project	`
Engineering team	Networking

{{#set:Feature priority=P1

|Feature rank=4 |Feature theme=Tracking Control |Feature roadmap=Privacy |Feature secondary roadmap=` |Feature list=Platform |Feature project=` |Feature engineering team=Networking }}

Team status notes

	status	notes
Products	`	`
Engineering	`	`
Security	`	`
Privacy	`	`
Localization	`	`
Accessibility	`	`
Quality assurance	`	`
User experience	`	`
Product marketing	`	`
Operations	`	`

{{#set:Feature products status=`

|Feature products notes=` |Feature engineering status=` |Feature engineering notes=` |Feature security status=` |Feature security health=` |Feature security notes=` |Feature privacy status=` |Feature privacy notes=` |Feature localization status=` |Feature localization notes=` |Feature accessibility status=` |Feature accessibility notes=` |Feature qa status=` |Feature qa notes=` |Feature ux status=` |Feature ux notes=` |Feature product marketing status=` |Feature product marketing notes=` |Feature operations status=` |Feature operations notes=` }}