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Envoy External Dependency Policy

Envoy has an evolving policy on external dependencies, tracked at envoyproxy#10471. This will become stricter over time, below we detail the policy as it currently applies.

External dependencies dashboard

The list of external dependencies in Envoy with their current version is available at https://www.envoyproxy.io/docs/envoy/latest/intro/arch_overview/security/external_deps

Declaring external dependencies

In general, all external dependencies for the Envoy proxy binary build and test should be declared in either bazel/repository_locations.bzl or api/bazel/repository_locations.bzl, unless listed under policy exceptions.

An example entry for the nghttp2 dependency is:

com_github_nghttp2_nghttp2 = dict(
    project_name = "Nghttp2",
    project_desc = "Implementation of HTTP/2 and its header compression ...",
    project_url = "https://nghttp2.org",
    version = "1.41.0",
    sha256 = "eacc6f0f8543583ecd659faf0a3f906ed03826f1d4157b536b4b385fe47c5bb8",
    strip_prefix = "nghttp2-{version}",
    urls = ["https://github.com/nghttp2/nghttp2/releases/download/v{version}/nghttp2-{version}.tar.gz"],
    use_category = ["dataplane"],
    last_updated = "2020-06-02",
    cpe = "cpe:2.3:a:nghttp2:nghttp2:*",
),

Dependency declarations must:

  • Provide a meaningful project name and URL.
  • State the version in the version field. String interpolation should be used in strip_prefix and urls to reference the version. If you need to reference version X.Y.Z as X_Y_Z, this may appear in a string as {underscore_version}, similarly for X-Y-Z you can use {dash_version}.
  • Versions should prefer release versions over main branch GitHub SHA tarballs. A comment is necessary if the latter is used. This comment should contain the reason that a non-release version is being used.
  • Provide accurate entries for use_category. Please think carefully about whether there are data or control plane implications of the dependency.
  • Reflect the UTC date (YYYY-MM-DD format) for the dependency release. This is when the dependency was updated in its repository. For dependencies that have releases, this is the date of the release. For dependencies without releases or for scenarios where we temporarily need to use a commit, this date should be the date of the commit in UTC.
  • CPEs are compulsory for all dependencies that are not purely build/test. CPEs provide metadata that allow us to correlate with related CVEs in dashboards and other tooling, and also provide a machine consumable join key. You can consult CPE search to find a CPE for a dependency."N/A" should only be used if no CPE for the project is available in the CPE database. CPEs should be versionless with a :* suffix, since the version can be computed from version.

When build or test code references Python modules, they should be specified via pip_install in bazel/repositories_extra.bzl. Python modules should not be listed in repository_locations.bzl entries. requirements.txt files for Python dependencies must pin to exact versions, e.g. PyYAML==5.4.1 and ideally also include a SHA256 checksum.

Pure developer tooling and documentation builds may reference Python via standalone requirements.txt, following the above policy.

New external dependencies

Any new dependency on the Envoy data or control plane that impacts Envoy core (i.e. is not specific to a single non-core extension) must be cleared with the Envoy dependency shepherds and security team, please file an issue and tag both dependency shepherds and the @envoyproxy/security-team.

The criteria below are used to evaluate new dependencies on the data, control and observability plane. They apply to all core dependencies and any extension that is robust to untrusted downstream or upstream traffic. The criteria are guidelines, exceptions may be granted with solid rationale. Precedent from existing extensions does not apply; there are extant extensions in violation of this policy which we will be addressing over time, they do not provide grounds to ignore policy criteria below.

Criteria Requirement Mnemonic Weight Rationale
Cloud Native Computing Foundation (CNCF) approved license MUST License High
Dependencies must not substantially increase the binary size unless they are optional (i.e. confined to specific extensions) MUST BinarySize High Envoy Mobile is sensitive to binary size. We should pick dependencies that are used in core with this criteria in mind.
No duplication of existing dependencies MUST NoDuplication High Avoid maintenance cost of multiple JSON parsers etc
Hosted on a git repository and the archive fetch must directly reference this repository. We will NOT support intermediate artifacts built by-hand located on GCS, S3, etc. MUST Source High Flows based on manual updates are fragile (they are not tested until needed), often suffer from missing documentation and shared exercise, may fail during emergency zero day updates and have no audit trail (i.e. it's unclear how the artifact we depend upon came to be at a later date).
CVE history appears reasonable, no pathological CVE arcs MUST SoundCVEs High Avoid dependencies that are CVE heavy in the same area (e.g. buffer overflow)
Code review (ideally PRs) before merge MUST Code-Review Normal Consistent code reviews
Security vulnerability process exists, with contact details and reporting/disclosure process MUST SecPolicy High Lack of a policy implies security bugs are open zero days
> 1 contributor responsible for a non-trivial number of commits MUST Contributors Normal Avoid bus factor of 1
Tests run in CI MUST CI-Tests Normal Changes gated on tests
High test coverage (also static/dynamic analysis, fuzzing) SHOULD Test-Coverage Normal Key dependencies must meet the same quality bar as Envoy
Envoy can obtain advanced notification of vulnerabilities or of security releases SHOULD SecPolicy-Compat High Coordinated security releases possible, but most dependencies do not feature this.
Do other significant projects have shared fate by using this dependency? SHOULD SharedFate High Increased likelihood of security community interest, many eyes.
Releases (with release notes) SHOULD Releases Normal Discrete upgrade points, clear understanding of security implications. We have many counterexamples today (e.g. CEL, re2).
Commits/releases in last 90 days SHOULD Active Normal Avoid unmaintained deps, not compulsory since some code bases are “done”

The rationale behind this policy is tracked here.

Maintaining existing dependencies

We rely on community volunteers to help track the latest versions of dependencies. On a best effort basis:

  • Core Envoy dependencies will be updated by the Envoy maintainers/security team.

  • Extension CODEOWNERS should update extension specific dependencies.

Where possible, we prefer the latest release version for external dependencies, rather than main branch GitHub SHA tarballs.

Dependency shepherds

Sign-off from the dependency shepherds is required for every PR that modifies external dependencies. The shepherds will look to see that the policy in this document is enforced and that metadata is kept up-to-date.

Dependency patches

Occasionally it is necessary to introduce an Envoy-side patch to a dependency in a .patch file. These are typically applied in bazel/repositories.bzl. Our policy on this is as follows:

  • Patch files impede dependency updates. They are expedient at creation time but are a maintenance penalty. They reduce the velocity and increase the effort of upgrades in response to security vulnerabilities in external dependencies.

  • No patch will be accepted without a sincere and sustained effort to upstream the patch to the dependency's canonical repository.

  • There should exist a plan-of-record, filed as an issue in Envoy or the upstream GitHub tracking elimination of the patch.

  • Every patch must have comments at its point-of-use in bazel/repositories.bzl providing a rationale and detailing the tracking issue.

Policy exceptions

The following dependencies are exempt from the policy:

  • Any developer-only facing tooling or the documentation build.

  • Transitive build time dependencies, e.g. Go projects vendored into protoc-gen-validate.