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Security Features

2 months ago6 min read
On This Page
  • Overview
  • Encryption
  • Sandboxing
  • Integrations
  • Audit logs

This document outlines security features built into CircleCI and related integrations.


Security is our top priority at CircleCI, we are proactive and we act on security issues immediately. Report security issues to with an encrypted message using our security team’s GPG key (ID: 0x4013DDA7, fingerprint: 3CD2 A48F 2071 61C0 B9B7 1AE2 6170 15B8 4013 DDA7).


CircleCI uses HTTPS or SSH for all networking in and out of our service including from the browser to our services application, from the services application to your builder fleet, from our builder fleet to your source control system, and all other points of communication. In short, none of your code or data travels to or from CircleCI without being encrypted unless you have code in your builds that does so at your discretion. Operators may also choose to go around our SSL configuration or not use TLS for communicating with underlying systems.

The nature of CircleCI is that our software has access to your code and whatever data that code interacts with. All jobs on CircleCI run in a sandbox (specifically, a Docker container or an ephemeral VM) that stands alone from all other builds and is not accessible from the Internet or from your own network. The build agent pulls code via git over SSH. Your particular test suite or job configurations may call out to external services or integration points within your network, and the response from such calls will be pulled into your jobs and used by your code at your discretion. After a job is complete, the container that ran the job is destroyed and rebuilt. All environment variables are encrypted using HashiCorp Vault. Environment variables are encrypted using AES256-GCM96 and are unavailable to CircleCI employees.


With CircleCI you control the resources allocated to run the builds of your code. This will be done through instances of our builder boxes that set up the containers in which your builds will run. By their nature, build containers will pull down source code and run whatever test and deployment scripts are part of the code base or your configuration. The containers are sandboxed, each created and destroyed for one build only (or one slice of a parallel build), and they are not available from outside themselves. The CircleCI service provides the ability to SSH directly to a particular build container. When doing this a user will have complete access to any files or processes being run inside that build container, so provide access to CircleCI only to those also trusted with your source code.


A few different external services and technology integration points touch CircleCI. The following list enumerates those integration points.

  • Web Sockets We use Pusher client libraries for WebSocket communication between the server and the browser, though for installs we use an internal server called slanger, so Pusher servers have no access to your instance of CircleCI nor your source control system. This is how we, for instance, update the builds list dynamically or show the output of a build line-by-line as it occurs. We send build status and lines of your build output through the web socket server (which unless you have configured your installation to run without SSL is done using the same certs over SSL), so it is encrypted in transit.

  • Replicated For private installations of CircleCI Server, Replicated is used to manage the installation wizard, licensing keys, system audit logs, software updates, and other maintenance and systems tasks for CircleCI. Your instance of CircleCI Server communicates with Replicated servers to send license key information and version information to check for updates. Replicated does not have access to your data or other systems, and CircleCI does not send any of your data to Replicated.

  • Source Control Systems To use CircleCI you will set up a direct connection with your instance of GitHub Enterprise,, or other source control system. When you set up CircleCI you authorize the system to check out your private repositories. You may revoke this permission at any time through your GitHub application settings page and by removing Circle’s Deploy Keys and Service Hooks from your repositories’ Admin pages. While CircleCI allows you to selectively build your projects, GitHub’s permissions model is “all or nothing” — CircleCI gets permission to access all of a user’s repositories or none of them. Your instance of CircleCI will have access to anything hosted in those git repositories and will create webhooks for a variety of events (eg: when code is pushed, when a user is added, etc.) that will call back to CircleCI, triggering one or more git commands that will pull down code to your build fleet.

  • Dependency and Source Caches Most CircleCI customers use S3 or equivalent cloud-based storage inside their private cloud infrastructure (Amazon VPC, etc) to store their dependency and source caches. These storage servers are subject to the normal security parameters of anything stored on such services, meaning in most cases our customers prevent any outside access.

  • Artifacts To help prevent other builds from accessing your browser local storage when viewing artifacts, HTML and XHTML pages are hosted on their own project-specific subdomain of * Non-HTML artifacts will usually be (302 FOUND) redirected to an S3 URL to allow for the highest download speed. Because these artifact types are hosted on a single S3 domain, artifacts may access your browser local storage on HTML and XHTML pages, and so you should avoid entering sensitive data into your browser for these URLs.

  • iOS Builds If you are paying to run iOS builds on CircleCI hardware your source code will be downloaded to a build box on our macOS fleet where it will be compiled and any tests will be run. Similar to our primary build containers that you control, the iOS builds we run are sandboxed such that they cannot be accessed.

  • Docker If you are using Docker images, refer to the public Docker seccomp (security computing mode) profile for the Docker engine. CircleCI appends the following to the Docker default seccomp profile:

    "comment": "Allow create user namespaces",
    "names": [
    "action": "SCMP_ACT_ALLOW",
    "args": [],
    "includes": {},
    "excludes": {}

Audit logs

CircleCI Server customers can access the audit log feature from the UI. Cloud customers can contact CircleCI support to request an Audit log. Note: only organization admin users can make an audit log request.

CircleCI logs important events in the system for audit and forensic analysis purposes. Audit logs are separate from system logs that track performance and network metrics.

Complete Audit logs may be downloaded from the Audit Log page within the Admin section of the application as a CSV file. Audit log fields with nested data contain JSON blobs.

Note: In some situations, the internal machinery may generate duplicate events in the audit logs. The id field of the downloaded logs is unique per event and can be used to identify duplicate entries.

Per our data retention policy, audit logs can be retrieved for up to 12 months.

Audit log events

Following are the system events that are logged. See action in the Field section below for the definition and format.

  • context.create
  • context.delete
  • context.env_var.delete
  • project.env_var.create
  • project.env_var.delete
  • project.settings.update
  • project.ssh_key.create
  • project.ssh_key.delete
  • project.api_token.create
  • schedule.create
  • schedule.update
  • schedule.delete
  • user.create
  • user.logged_in
  • user.logged_out
  • workflow.job.approve
  • workflow.job.finish
  • workflow.job.scheduled
  • workflow.job.start

Audit log fields

  • action: The action taken that created the event. The format is ASCII lowercase words separated by dots, with the entity acted upon first and the action taken last. In some cases entities are nested, for example, workflow.job.start.
  • actor: The actor who performed this event. In most cases this will be a CircleCI user. This data is a JSON blob that will always contain id and and type and will likely contain name.
  • target: The entity instance acted upon for this event, for example, a project, an org, an account, or a build. This data is a JSON blob that will always contain id and and type and will likely contain name.
  • payload: A JSON blob of action-specific information. The schema of the payload is expected to be consistent for all events with the same action and version.
  • occurred_at: When the event occurred in UTC expressed in ISO-8601 format with up to nine digits of fractional precision, for example ‘2017-12-21T13:50:54.474Z’.
  • metadata: A set of key/value pairs that can be attached to any event. All keys and values are strings. This can be used to add additional information to certain types of events.
  • id: A UUID that uniquely identifies this event. This is intended to allow consumers of events to identify duplicate deliveries.
  • version: Version of the event schema. Currently the value will always be 1. Later versions may have different values to accommodate schema changes.
  • scope: If the target is owned by an Account in the CircleCI domain model, the account field should be filled in with the Account name and ID. This data is a JSON blob that will always contain id and type and will likely contain name.
  • success: A flag to indicate if the action was successful.
  • request: If this event was triggered by an external request this data will be populated and may be used to connect events that originate from the same external request. The format is a JSON blob containing id (the unique ID assigned to this request by CircleCI).

See also

GitHub and Bitbucket Integration

Help make this document better

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