Security Bug Approval Process

How to fix a core-security bug in Firefox - developer guidelines

Follow these security guidelines if you’re involved in reviewing, testing and landing a security patch: Fixing Security Bugs.

Purpose: don’t 0-day ourselves

People watch our check-ins. They may be able to start exploiting our users before we can get an update out to them if

  • the patch is an obvious security fix (bounds check, kungFuDeathGrip, etc.)

  • the check-in comment says “security fix” or includes trigger words like “exploitable”, “vulnerable”, “overflow”, “injection”, “use after free”, etc.

  • comments in the code mention those types of things or how someone could abuse the bug

  • the check-in contains testcases that show exactly how to trigger the vulnerability

Principle: assume the worst

  • If there’s no rating we assume it could be critical

  • If we don’t know the regression range we assume it needs porting to all supported branches

Process for Security Bugs (Developer Perspective)

Filing / Managing Bugs

  • Try whenever possible to file security bugs marked as such when filing, instead of filing them as open bugs and then closing later. This is not always possible, but attention to this, especially when filing from crash-stats, is helpful.

  • It is _ok_ to link security bugs to non-security bugs with Blocks, Depends, Regressions, or See Also. Users with the editbugs permission will be able to see the reference, but not view a restricted bug or its summary. Users without the permission will not be able to see the link. For critical severity bugs where even that seems problematic, consider mentioning the bug in a comment on the security bug instead. We can always fill in the links later after the fix has shipped.

Developing the Patch

  • Comments in the code should not mention a security issue is being fixed. Don’t paint a picture or an arrow pointing to security issues any more than the code changes already do.

  • Do not push to Try servers if possible: this exposes the security issues for these critical and high rated bugs to public viewing. In an ideal case, testing of patches is done locally before final check-in to mozilla-central.

  • If pushing to Try servers is necessary, do not include the bug number in the patch. Ideally, do not include tests in the push as the tests can illustrate the exact nature of the security problem frequently.

  • If you must push to Try servers, with or without tests, try to obfuscate what this patch is for. Try to push it with other, non-security work, in the same area.

Request review of the patch in the same process as normal. After the patch has been reviewed you will request sec-approval as needed. See Fixing Security Bugs for more examples/details of these points.

Preparing the patch for landing

See Fixing Security Bugs for more details.

On Requesting sec-approval

For security bugs with no sec- severity rating assume the worst and follow the rules for sec-critical. During the sec-approval process we will notice it has not been rated and rate it during the process.

Core-security bug fixes can be landed by a developer without any explicit approval if:

A) The bug has a sec-low, sec-moderate, sec-other, or sec-want rating.
B) The bug is a recent regression on mozilla-central. This means
  • A specific regressing check-in has been identified

  • The developer can (and has) marked the status flags for ESR and Beta as “unaffected”

  • We have not shipped this vulnerability in anything other than a nightly build

If it meets the above criteria, developers do not need to ask for sec-approval.

In all other cases, developers should ask for sec-approval. When a patch is ready to be landed, click on the “Details” link for it in the Bugzilla attachment table (not directly on phabricator at time of writing), then set the sec-approval flag to ‘?’.

If developers are unsure about a bug and it has a patch ready, just request sec-approval anyway and move on. Don’t overthink it!

An automatic nomination comment will be added to bugzilla when sec-approval is set to ‘?’. The questions in this need to be filled out as best as possible when sec-approval is requested for the patch.

It is as follows (courtesy of Dan Veditz):

[Security approval request comment]
How easily can the security issue be deduced from the patch?
Do comments in the patch, the check-in comment, or tests included in
the patch paint a bulls-eye on the security problem?
Which older supported branches are affected by this flaw?
If not all supported branches, which bug introduced the flaw?
Do you have backports for the affected branches? If not, how
different, hard to create, and risky will they be?
How likely is this patch to cause regressions; how much testing does
it need?

This is similar to the ESR approval nomination form and is meant to help us evaluate the risks around approving the patch for checkin.

When the bug is approved for landing, the sec-approval flag will be set to ‘+’ with a comment from the approver to land the patch. At that point, land it according to instructions provided..

This will allow us to control when we can land security bugs without exposing them too early and to make sure they get landed on the various branches.

If you have any questions or are unsure about anything in this document contact us on Slack in the #security channel or the current sec-approvers Dan Veditz and Tom Ritter.

Process for Security Bugs (sec-approver Perspective)

The security assurance team and release management will have their own process for approving bugs:

  1. The Security assurance team goes through sec-approval ? bugs daily and approves low risk fixes for central (if early in cycle). Developers can also ping the Security Assurance Team (specifically Tom Ritter & Dan Veditz) in #security on Slack when important.

    1. If a bug lacks a security-rating one should be assigned - possibly in coordination with the (other member of) the Security Assurance Team

  2. Security team marks tracking flags to ? for all affected versions when approved for central. (This allows release management to decide whether to uplift to branches just like always.)

  3. Weekly security/release management triage meeting goes through sec-approval + and ? bugs where beta and ESR is affected, ? bugs with higher risk (sec-high and sec-critical), or ? bugs near end of cycle.

Options for sec-approval including a logical combination of the following:

  • Separate out the test and comments in the code into a followup commit we will commit later.

  • Remove the commit message and place it in the bug or comments in a followup commit.

  • Please land it bundled in with another commit

  • Land today

  • Land today, land the tests after

  • Land closer to the release date

  • Land in Nightly to assess stability

  • Land today and request uplift to all branches

  • Request uplift to all branches and we’ll land as close to shipping as permitted

  • Chemspill time

The decision process for which of these to choose is perceived risk on multiple axes:

  • ease of exploitation

  • reverse engineering risk

  • stability risk

The most common choice is: not much stability risk, not an immediate reverse engineering risk, moderate to high difficulty of exploitation: “land whenever”.