GitHub Desktop Vulnerability Risks Credential Leaks via Malicious Remote URLs

Affected versions of Git have a vulnerability whereby Git can be tricked into sending private credentials to a host controlled by an attacker. Git uses external "credential helper" programs to store and retrieve passwords or other credentials from secure storage provided by the operating system. Specially-crafted URLs that contain an encoded newline can inject unintended values into the credential helper protocol stream, causing the credential helper to retrieve the password for one server (e.g., good.example.com) for an HTTP request being made to another server (e.g., evil.example.com), resulting in credentials for the former being sent to the latter. There are no restrictions on the relationship between the two, meaning that an attacker can craft a URL that will present stored credentials for any host to a host of their choosing. The vulnerability can be triggered by feeding a malicious URL to git clone. However, the affected URLs look rather suspicious; the likely vector would be through systems which automatically clone URLs not visible to the user, such as Git submodules, or package systems built around Git. The problem has been patched in the versions published on April 14th, 2020, going back to v2.17.x. Anyone wishing to backport the change further can do so by applying commit 9a6bbee (the full release includes extra checks for git fsck, but that commit is sufficient to protect clients against the vulnerability). The patched versions are: 2.17.4, 2.18.3, 2.19.4, 2.20.3, 2.21.2, 2.22.3, 2.23.2, 2.24.2, 2.25.3, 2.26.1.

Git Credential Manager (GCM) is a secure Git credential helper built on .NET that runs on Windows, macOS, and Linux. The Git credential protocol is text-based over standard input/output, and consists of a series of lines of key-value pairs in the format `key=value`. Git's documentation restricts the use of the NUL (`\0`) character and newlines to form part of the keys or values. When Git reads from standard input, it considers both LF and CRLF as newline characters for the credential protocol by virtue of calling `strbuf_getline` that calls to `strbuf_getdelim_strip_crlf`. Git also validates that a newline is not present in the value by checking for the presence of the line-feed character (LF, `\n`), and errors if this is the case. This captures both LF and CRLF-type newlines. Git Credential Manager uses the .NET standard library `StreamReader` class to read the standard input stream line-by-line and parse the `key=value` credential protocol format. The implementation of the `ReadLineAsync` method considers LF, CRLF, and CR as valid line endings. This is means that .NET considers a single CR as a valid newline character, whereas Git does not. This mismatch of newline treatment between Git and GCM means that an attacker can craft a malicious remote URL. When a user clones or otherwise interacts with a malicious repository that requires authentication, the attacker can capture credentials for another Git remote. The attack is also heightened when cloning from repositories with submodules when using the `--recursive` clone option as the user is not able to inspect the submodule remote URLs beforehand. This issue has been patched in version 2.6.1 and all users are advised to upgrade. Users unable to upgrade should only interact with trusted remote repositories, and not clone with `--recursive` to allow inspection of any submodule URLs before cloning those submodules.

Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals. When Git asks for credentials via a terminal prompt (i.e. without using any credential helper), it prints out the host name for which the user is expected to provide a username and/or a password. At this stage, any URL-encoded parts have been decoded already, and are printed verbatim. This allows attackers to craft URLs that contain ANSI escape sequences that the terminal interpret to confuse users e.g. into providing passwords for trusted Git hosting sites when in fact they are then sent to untrusted sites that are under the attacker's control. This issue has been patch via commits `7725b81` and `c903985` which are included in release versions v2.48.1, v2.47.2, v2.46.3, v2.45.3, v2.44.3, v2.43.6, v2.42.4, v2.41.3, and v2.40.4. Users are advised to upgrade. Users unable to upgrade should avoid cloning from untrusted URLs, especially recursive clones.

Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals. Git defines a line-based protocol that is used to exchange information between Git and Git credential helpers. Some ecosystems (most notably, .NET and node.js) interpret single Carriage Return characters as newlines, which renders the protections against CVE-2020-5260 incomplete for credential helpers that treat Carriage Returns in this way. This issue has been addressed in commit `b01b9b8` which is included in release versions v2.48.1, v2.47.2, v2.46.3, v2.45.3, v2.44.3, v2.43.6, v2.42.4, v2.41.3, and v2.40.4. Users are advised to upgrade. Users unable to upgrade should avoid cloning from untrusted URLs, especially recursive clones.

Git LFS is a Git extension for versioning large files. When Git LFS requests credentials from Git for a remote host, it passes portions of the host's URL to the `git-credential(1)` command without checking for embedded line-ending control characters, and then sends any credentials it receives back from the Git credential helper to the remote host. By inserting URL-encoded control characters such as line feed (LF) or carriage return (CR) characters into the URL, an attacker may be able to retrieve a user's Git credentials. This problem exists in all previous versions and is patched in v3.6.1. All users should upgrade to v3.6.1. There are no workarounds known at this time.

The gh cli is GitHub’s official command line tool. A security vulnerability has been identified in the GitHub CLI that could leak authentication tokens when cloning repositories containing `git` submodules hosted outside of GitHub.com and ghe.com. This vulnerability stems from several `gh` commands used to clone a repository with submodules from a non-GitHub host including `gh repo clone`, `gh repo fork`, and `gh pr checkout`. These GitHub CLI commands invoke git with instructions to retrieve authentication tokens using the `credential.helper` configuration variable for any host encountered. Prior to version `2.63.0`, hosts other than GitHub.com and ghe.com are treated as GitHub Enterprise Server hosts and have tokens sourced from the following environment variables before falling back to host-specific tokens stored within system-specific secured storage: 1. `GITHUB_ENTERPRISE_TOKEN`, 2. `GH_ENTERPRISE_TOKEN` and 3. `GITHUB_TOKEN` when the `CODESPACES` environment variable is set. The result being `git` sending authentication tokens when cloning submodules. In version `2.63.0`, these GitHub CLI commands will limit the hosts for which `gh` acts as a credential helper to source authentication tokens. Additionally, `GITHUB_TOKEN` will only be used for GitHub.com and ghe.com. Users are advised to upgrade. Additionally users are advised to revoke authentication tokens used with the GitHub CLI and to review their personal security log and any relevant audit logs for actions associated with their account or enterprise

GitHub Desktop is an open-source Electron-based GitHub app designed for git development. An attacker convincing a user to clone a repository directly or through a submodule can allow the attacker access to the user's credentials through the use of maliciously crafted remote URL. GitHub Desktop relies on Git to perform all network related operations (such as cloning, fetching, and pushing). When a user attempts to clone a repository GitHub Desktop will invoke `git clone` and when Git encounters a remote which requires authentication it will request the credentials for that remote host from GitHub Desktop using the git-credential protocol. Using a maliciously crafted URL it's possible to cause the credential request coming from Git to be misinterpreted by Github Desktop such that it will send credentials for a different host than the host that Git is currently communicating with thereby allowing for secret exfiltration. GitHub username and OAuth token, or credentials for other Git remote hosts stored in GitHub Desktop could be improperly transmitted to an unrelated host. Users should update to GitHub Desktop 3.4.12 or greater which fixes this vulnerability. Users who suspect they may be affected should revoke any relevant credentials.