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

Low severity GitHub Reviewed Published Aug 31, 2024 in Byron/gitoxide • Updated Sep 3, 2024

Package

cargo gix-path (Rust)

Affected versions

< 0.10.10

Patched versions

0.10.10

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 configuration file truly associated with the installation is not present on all systems and can occasionally be empty. Likewise, there may be no variables in the global scope.
  • Configuration files associated with those higher scopes may be deliberately skipped by setting the GIT_CONFIG_SYSTEM and GIT_CONFIG_GLOBAL environment variables to /dev/null (or to NUL on Windows). This prevents gix-path from finding the path of configuration files for those scopes, while not preventing downstream components such as the function in gix-config from reporting a local path as being associated with the installation.
  • The GIT_CONFIG_NOSYSTEM environment variable can be used to disable configuration associated with the installation. (GIT_CONFIG_NOSYSTEM=1 is more powerful than GIT_CONFIG_SYSTEM=/dev/null on systems where an additional "unknown" scope is associated with the installation, as occurs on macOS with Apple Git.) This will cause the local scope to be the highest nonempty scope under even more situations, though in practice it is less dangerous because most, though possibly not all, downstream components would disregard the value.

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:

  • A less secure configuration may be set for a specific repository where it is judged acceptable, even though it would not be wanted for other repositories, such as to enable a protocol or set up debugging.
  • More likely, a configuration that supplies secrets for use in one repository's remote can be used to send those secrets to another repository's remote.

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 (12251eb052df30105538fa831e641eea557f13d8 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.

References

@Byron Byron published to Byron/gitoxide Aug 31, 2024
Published by the National Vulnerability Database Sep 2, 2024
Published to the GitHub Advisory Database Sep 3, 2024
Reviewed Sep 3, 2024
Last updated Sep 3, 2024

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity High
Attack Requirements None
Privileges Required None
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality Low
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:H/AT:N/PR:N/UI:P/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

EPSS score

0.045%
(16th percentile)

Weaknesses

CVE ID

CVE-2024-45305

GHSA ID

GHSA-v26r-4c9c-h3j6

Source code

Credits

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