Security/Features/Browser CRL

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Browser CRL
Stage Draft
Status In progress
Release target `
Health OK
Status note `


Product manager SId Stamm
Directly Responsible Individual David Keeler
Lead engineer David Keeler
Security lead Curtis Koenig
Privacy lead Sid Stamm
Localization lead `
Accessibility lead `
QA lead `
UX lead `
Product marketing lead `
Operations lead `
Additional members `

Open issues/risks


Stage 1: Definition

1. Feature overview

Implement a revocation list push mechanism in Firefox, which will push revocation lists of certificates to Firefox browsers on a regular basis, asynchronously and independently of any SSL site visit. This will improve security by ensuring the browser has a comprehensive list of revocations in a manner that is not likely to be blocked by a network attacker.

We should be able to use this revocation push mechanism to quickly revoke (distrust) root certificates, intermediate certificates, and end-entity certificates.

Every time we have to distrust a certificate for any reason (such as a security compromise or an instance of MITM) we either have to create an emergency update or quickly get it into an upcoming release (when the timing works in our favor and allows us to do so). We need to make it less costly, easier, and faster to distrust certificates.

When a CA revokes an intermediate certificate due to a security concern, Mozilla should give an Untrusted Connection error for websites with certs signed by the revoked intermediate certificate.

When a CA revokes an end-entity certificate due to a security concern, Mozilla should give an Untrusted Connection error for websites with that SSL certs.

2. Users & use cases

There are currently three use cases this feature addresses:

  1. A CA is no longer trusted (in its entirety), so needs to be treated as revoked.
  2. A CA's intermediate certificate is no longer trusted, so needs to be treated as revoked.
  3. The key of an end-entity certificate belonging to a high-profile entity is compromised (e.g. a bank, government, etc.), so needs to be treated as revoked.

Instead of spinning up and releasing a binary update, we simply add entries as appropriate to the Browser CRL. Next time the user's browser pings us for updates, we ship them the new Browser CRL and the changes instantly take effect.

3. Dependencies


4. Requirements

  1. The ability to revoke (and treat as revoked) root certificates, intermediate certificates, and end-entity certificates.
  2. The ability to use specific keys to identify which certificates to treat as revoked.
  3. The ability to undo a block should one be applied erroneously


This will not serve the same purpose as shipping a white-list of all intermediate certificates, which is another proposal under discussion.

This does not solve revocation in general. We will not add Joe Schmoe's compromised server certificate to the blocklist.

Stage 2: Design

5. Functional specification


6. User experience design

There should not be any UX changes.

Stage 3: Planning

7. Implementation plan

Previously this feature request was called "Cert BLocklist via Update Ping"

It was originally thought that the easiest way to implement this feature would be to piggyback on the blocklist. Whoever works on creating this Browser CRL feature should consider that, as well as other implementation strategies.

8. Reviews

Security review


Privacy review


Localization review




Quality Assurance review


Operations review


Stage 4: Development

9. Implementation


Stage 5: Release

10. Landing criteria


Feature details

Priority P2
Rank 999
Theme / Goal Product Hardening
Roadmap Security
Secondary roadmap Platform
Feature list `
Project `
Engineering team Security

Team status notes

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