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RUSTSEC-2024-0367

gix-path uses local config across repos when it is the highest scope

Reported
Issued
Package
gix-path (crates.io)
Type
Vulnerability
Keywords
#configuration-failure #information-leak
Aliases
References
CVSS Score
2.5 LOW
CVSS Details
Attack vector
Local
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None
CVSS Vector
CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:L/I:N/A:N
Patched
  • >=0.10.10
Affected Functions
Version
gix_path::env::installation_config
  • *
gix_path::env::installation_config_prefix
  • *

Description

Summary

gix-path executes git to find the path of a configuration file that belongs to the git installation itself, but mistakenly treats the local repository's configuration as system-wide if no higher scoped configuration is found. In rare cases, this causes a less trusted repository to be treated as more trusted, or leaks sensitive information from one repository to another, such as sending credentials to another repository's remote.

Details

In gix_path::env, the underlying implementation of the installation_config and installation_config_prefix functions calls git config -l --show-origin and parses the first line of the output to extract the path to the configuration file holding the configuration variable of highest scope:

https://github.com/Byron/gitoxide/blob/12251eb052df30105538fa831e641eea557f13d8/gix-path/src/env/git/mod.rs#L91

https://github.com/Byron/gitoxide/blob/12251eb052df30105538fa831e641eea557f13d8/gix-path/src/env/git/mod.rs#L112

While the configuration variable of highest scope is not usually in the local scope, there are practical situations where this occurs:

A user may use either or both of the latter two techniques to turn off an undesired configuration or to create a more replicable environment. Such a user would expect that this results in a more controlled configuration.

Often, when located inside one repository, a user performs operations on that repository or that are not specific to any repository. In such use, local configuration is typically desired or at least acceptable, and mistaking it as coming from another scope is not typically harmful.

However, sometimes a user is in one repository and operates on another repository. A major case where this occurs is cloning one repository while located in another. This can be done in an ad-hoc fashion, including when cloning the repository outside of the one we are inside. It may also potentially be automated by an application for purposes such as submodule handling. Two kinds of problems are anticipated:

PoC

In this example, we send mock Authorization: Basic ... credentials meant for one repository's remote to another remote, by running gix while inside the first repository to clone the second repository.

These instructions are written for a Unix shell, but they will work in other shells, including in PowerShell on Windows if the method of setting environment variables is adapted and /dev/null is replaced with NUL. This procedure is likely to demonstrate the problem on all systems except macOS. This is due to the high-scoped "unknown" configuration that usually accompanies Apple Git, and reflects that gix-path is in practice much less vulnerable on macOS (though still potentially vulnerable).

  1. Install dummyhttp to serve as a local HTTP server for the demonstration.

  2. Obtain a build of gitoxide with the max feature set enabled. While this vulnerability affects other builds, this example requires max for http.extraHeader support.

    Running cargo install gitoxide will install such a build though it may build against a patched version of gix-path. Cloning the repository (12251eb and earlier are affected) and building with cargo build or cargo install --path . are also sufficient. In contrast, installing from published binaries with binstall or quickinstall does not provide the max feature, as of this writing.

  3. Run: dummyhttp -i 127.0.0.1 -c 403 -v

  4. In a separate terminal, create a new local repository and set up a mock remote and http.extraHeader configuration:

    git init myrepo
    cd myrepo
    git remote add origin http://127.0.0.1:8080/mygit.git
    git config --local http.extraHeader 'Authorization: Basic abcde'
    
  5. Make sure the testing setup is working by running gix fetch in the repository and checking that it fails in the expected way. In the terminal where that is run, a message should be shown indicating an HTTP 403 error. The more interesting output is in the terminal where dummyhttp is running, which should look like this:

    2024-30-30 03:30:16 127.0.0.1:55689 GET /myrepo.git/info/refs?service=git-upload-pack HTTP/1.1
    ┌─Incoming request
    │ GET /myrepo.git/info/refs?service=git-upload-pack HTTP/1.1
    │ Accept: */*
    │ Authorization: Basic abcde
    │ Git-Protocol: version=2
    │ Host: 127.0.0.1:8080
    │ User-Agent: git/oxide-0.42.2
    ┌─Outgoing response
    │ HTTP/1.1 403 Forbidden
    │ Content-Length: 9
    │ Content-Type: text/plain; charset=utf-8
    │ Date: Fri, 30 Aug 2024 03:30:16 -0400
    

    Some details may differ, especially dates and times. But Authorization: Basic abcde should be shown.

  6. Now, in the terminal where you ran gix fetch, try cloning a separate repository:

    gix clone http://127.0.0.1:8080/other.git
    

    Check the output appended in the terminal where dummyhttp is running. This is to observe that Authorization: Basic abcde was rightly not sent.

    Alternatively, if it does appear, then your system may be in one of the uncommon configurations that is vulnerable without further action.

  7. Now rerun that command, but with a modified environment, to cause gix-path to wrongly treat configuration from the local scope as being associated with the git installation:

    env GIT_CONFIG_SYSTEM=/dev/null GIT_CONFIG_GLOBAL=/dev/null gix clone http://127.0.0.1:8080/other.git
    

    Check the output appended in the terminal where dummyhttp is running. Observe that Authorization: Basic abcde was wrongly sent.

While this procedure uses the same remote host for both repositories, this is not a required element. If the second repository had a different, untrusted host, the extra header would still be sent.

Impact

It is believed to be very difficult to exploit this vulnerability deliberately, due to the need either to anticipate a situation in which higher-scoped configuration variables would be absent, or to arrange for this to happen. Although any operating system may be affected, users running Apple Git on macOS are much less likely to be affected.

In the example shown above, more secure general practices would avoid it: using a credential manager, or even using http.<url>.extraHeader with as specific a <url> as possible, rather than the more general http.extraHeader. Many scenarios are analogous: if each repository's configuration is as secure as possible for how the repository is used, and secrets are stored securely and separately, then the circumstances under which an unacceptably unsecure configuration is used, or under which a leak of credentials would occur, become unlikely.

Advisory available under CC0-1.0 license.