GitHub.com

Synopsis

GitHub.com is our main web site. It is our most intricate application with a number of user inputs and access methods. GitHub.com is built on Ruby on Rails and leverages a number of Open Source technologies.

Focus areas

Ineligible submissions

Including HTML in Markdown content

Many areas of GitHub allow content formatted in GitHub Flavored Markdown. It is intended that these Markdown fields allow a limited subset of HTML, such as <b>, <sup> and <details>. HTML included by users in Markdown fields is filtered for malicious input such as <script>, so this does not present a security risk.

Leaking email addresses via .patch links

.patch links on GitHub show the raw commit diff, similar to git-format-patch, and intentionally show the email address used by the author. The email address shown in .patch links is configured by the user with git-config on their local machine. To hide email addresses from Git operations, such as .patch links, users can set the Keep my email address private and Block command line pushes that expose my email options. More details are available in our About Commit Email Addresses documentation.

Phishing using Unicode homoglyphs or RTLO characters

We are aware of different ways that Unicode - specifically homoglyphs and RTLO characters - can be used to display misleading information to other GitHub users. We consider these low-risk and ineligible for a reward. If you have noticed someone using GitHub for phishing, please let us know.

Email verification policy

Any email address that is not already associated with an account on GitHub may be claimed and this will give commit attribution to the claiming user. While we allow this attribution without requiring email address verification, any disputes around emails on accounts can be resolved by contacting our support team.

Impersonating a user through git email address

Because Git is a distributed version control system, GitHub must use the commit email address to assign attribution. When you push a repository to GitHub.com it may contain one or more commits, some of which you may not have authored. For example, imagine a scenario where you collaborated with a number of people on a git repository before you made your first push of that repository to GitHub.com. This push would contain a number of commits from several authors. It would be incorrect to assign all of the commits to the person doing the push, so we use the commit log email addresses to assign attribution on GitHub.com. Each subsequent push to GitHub uses this same logic to assign attribution of commit authors.

It’s important to note that impersonating another GitHub user in this fashion doesn’t grant you access to any of their repositories or give you any privileges you didn’t already have. However, GitHub does consider impersonation an account abuse issue that we take very seriously. If someone is wrongfully impersonating you, please let us know and we will investigate the matter and deal with it as quickly as we can. In addition, if you are still concerned about this, you and your team can choose to use Git’s built in options to sign commits with a GPG key (check out the git commit -S command).

DMARC, SPF and DKIM email policy

Our DMARC, SPF and DKIM settings are tuned to balance security against email deliverability concerns. We continue to evaluate our setup and may make this functionality more strict in the future.

Bypassing country restrictions for SMS two-factor authentication

The restriction on which countries are able to configure SMS two-factor authentication is based on SMS delivery reliability. We have removed countries we found to have low delivery success rates to prevent account lockout. Our validation is client-side and bypassing this validation does not present a security risk. Users in countries where SMS is unavailable can use an alternative two-factor authentication method

Vulnerabilities in repositories hosted on GitHub

GitHub users are responsible for the content hosted in their repositories. Any vulnerabilties in user content do not affect the security of GitHub.com or its users. We recommend that you report these vulnerabilities directly to the owner of the repository.

Host header injection

Host header injection reports are ineligible unless it can be shown to cause a specific security issue. We set the Strict-Transport-Security header, use HTTP public key pinning, and are in the browser preload lists which prevent active network attacks that may attempt to inject the header.

Timing attacks which reveal a private repository or user

There are architectural nuances that prevent us from systematically preventing timing attacks from determining if a specific repository exists, or if a specific user is part of a secret team, and are therefore ineligible.

Vulnerabilities caused by out-dated browsers

Vulnerabilities that don’t affect the latest version of modern browsers, such as Chrome, Firefox, Edge and Safari, are ineligible. Vulnerabilities caused by browser extensions are also ineligible.

Submit a vulnerability for GitHub.com

Recently collected GitHub.com bounties:

1 vyshakh 10000 pts Vyshakh Parakkat Repository imports defaulting to public regardless of user's visibility selection
2 brxxn 10000 pts brian Incorrect OAuth scopes shown on authorization page
3 asanso 1000 pts Antonio Sanso Creating verified commits for arbitrary emails using web commits
4 jonathanwalker 555 pts Jonathan Walker "Require review from Code Owners" bypass using unverified email addresses
5 staaldraad 20000 pts Etienne Stalmans RCE in GitHub Pages when building with submodules