Code owners
Overview
Github allows you to define for individuals or teams that are responsible for code in a repository or code owners. To do so, you should add the CODEOWNERS
file to one of the following locations:
.github/
/
docs/
After which you can set up rules for protected branches and require mandatory approval from code owners.
References:
Code ownership takeover
The documentation for code owners said that the CODEOWNERS
file can be defined in /
, docs/
, or .github/
directory:
However, what happens if a repository contains multiple CODEOWNERS files? Actually, among the allowed paths there is the following priority:
.github/
/
docs/
So, if Github finds CODEOWNERS
file in .github/
, it will ignore CODEOWNERS
files in /
and docs/
. In other words, if CODEOWNERS
file has been created in /
or docs/
, an attacker with write permissions is able to add CODEOWNERS
file to .github/
, takeover code ownership, and bypass branch protection rules.Now the attacker is the owner of the code of the entire repository and can approve any changes.
Suppose there is a repository where .github/
has separate owners who are responsible for changes to that directory and CODEOWNERS
file is stored in /
. In such case, the CODEOWNERS
file may look like this:
A member of the @dev-team
team, or an attacker who gains access to the account of this member, can elevate their privileges in this repository using the next steps:
Using a personal Github account or other compromised account fork the repository.
Add
.github/CODEOWNERS
file with the following content:Create a PR to the target repo.
Approve the PR (since an attacker has access to the account that is an code owner of the
.github/
, they can approve any changes within.github/
).Merge changes.
Now an attacker is a code owner for the whole repository and they are able to approve any changes, including those outside
.github/
.
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