Summary
gix-path
runs git
to find the path of a configuration file associated with the git
installation, but improperly resolves paths containing unusual or non-ASCII characters, in rare cases enabling a local attacker to inject configuration leading to code execution.
Details
In gix_path::env
, the underlying implementation of the installation_config
and installation_config_prefix
functions calls git config -l --show-origin
to find the path of a file to treat as belonging to the git
installation.
Affected versions of gix-path
do not pass -z
/--null
to cause git
to report literal paths (650a1b5
). Instead, to cover the occasional case that git
outputs a quoted path, they attempt to parse the path by stripping the quotation marks:
The problem is that, when a path is quoted, it may change in substantial ways beyond the concatenation of quotation marks. If not reversed, these changes can result in another valid path that is not equivalent to the original.
This is not limited to paths with unusual characters such as quotation marks or newlines. Unless git
is explicitly configured with core.quotePath
set to false
, it also happens when the path contains most non-ASCII characters, including accented or non-English letters. For example, é
is transformed to \303\251
, with literal backslashes. (This is an octal representation of the bytes in its UTF-8 encoding. This behavior is not limited to systems that encode paths with UTF-8 on disk.)
Rarely, the configuration file gix-path
wrongly attempts to open can be created by an attacker who has a limited user account on the system. The attacker would often need to request an account username tailored to carrying out the attack.
PoC
Quick demonstration on Unix
On a Unix-like system in which Git supports no higher scope than system
for configuration variables (i.e., not on macOS with Apple Git), in a locale that supports UTF-8, with gitoxide
installed, run:
mkdir myrepo
cd myrepo
git init
printf '[real]\n\trealvar = realval\n' > 'é'
printf '[fake]\n\tfakevar = fakeval\n' > '\303\251'
GIT_CONFIG_SYSTEM='é' gix config
If the above conditions are satisfied and the gix
command was built against an affected version of gix-path
, then the last command's output looks something like this:
# From '\303\251' (GitInstallation)
[fake]
fakevar = fakeval
# From 'é' (System)
[real]
realvar = realval
# From '/home/ubuntu/.gitconfig' (User)
[init]
defaultBranch = main
# From './.git/config' (Local)
[core]
repositoryformatversion = 0
filemode = true
bare = false
logallrefupdates = true
Demonstration across user accounts on Windows
On a test system running Windows on which Git for Windows is not installed system-wide—resembling a scenario in which users who wish to use Git are expected to install it themselves for their accounts—create two accounts, with these usernames:
- Renée, the target of the attack. This user may be a limited user or an administrator. Its user profile directory is assumed to be
C:\Users\Renée
. - Ren, the user who carries out the attack. This user should be a limited user, since an administrator would not need to exploit this vulnerability to inject configuration. Its user profile directory is assumed to be
C:\Users\Ren
.
As Ren, run these commands in PowerShell:
$d = "$HOME\303\251e\AppData\Local\Programs\Git\etc"
mkdir $d
git config --file $d\gitconfig core.sshCommand calc.exe
icacls $HOME\303 /grant 'Renée:(RX)' /T
(The gitconfig
file can instead be written manually, in which case Ren need not have git
.)
As Renée:
-
Install Git for Windows in the default location for non-systemwide installations, which for that user account is inside
C:\Users\Renée\AppData\Local\Programs
. For a non-administrative installation, Git for Windows will pick this location automatically. Allow the installer to place the directory containinggit
in the user'sPATH
, as it does by default.(The scenario can be modified for any location the attacker can predict. So, for example, Renée can install Git for Windows with
scoop
, and Ren could carry out the attack with correspondingly modified path components in place ofAppData\Local\Programs\Git
.) -
Install
gitoxide
using any common technique, such as by installing Rust and then runningcargo install gitoxide
. -
Open a PowerShell window and run a
gix
command that attempts to run the SSH client for transport. For example:gix clone ssh://localhost/myrepo.git
At least one, and usually two, instances of the Windows calculator will pop up. This happens because
calc.exe
was configured in the fake configuration file the user Ren was able to cause to be used, by placing it at the locationgix-path
wrongly resolved the path of Renée's own configuration file to.
The gitconfig
file written by the attacker can be adjusted with an arbitrary choice of payload, or to set other configuration variables.
Impact
On a single-user system, it is not possible to exploit this, unless GIT_CONFIG_SYSTEM
and GIT_CONFIG_GLOBAL
have been set to unusual values or Git has been installed in an unusual way. Such a scenario is not expected.
Exploitation is unlikely even on a multi-user system, though it is plausible in some uncommon configurations or use cases. It is especially unlikely with Apple Git on macOS, due to its very high scoped configuration in /Library
or /Applications
that would be detected instead, as in CVE-2024-45305.
The likelihood of exploitation may be higher on Windows, where attacks such as those shown in the Windows proof-of-concept above can be performed due to the status of \
as a directory separator, and where there is no restriction on usernames containing accented or non-English letters (though the latter is also permitted on some other systems). Even then, complex user interaction is required. In most cases, a system administrator would have to approve an innocuous-seeming username, and then the targeted user (who could be the same or a different user) would have to use an application that uses gix-path
.
In general, exploitation is more likely to succeed if at least one of the following applies:
- Users are expected to install
git
themselves, and are likely to do so in predictable locations. - Locations where
git
is installed, whether due to usernames in their paths or otherwise, contain characters thatgit
quotes by default in paths, such as non-English letters and accented letters. - A custom
system
-scope configuration file is specified with theGIT_CONFIG_SYSTEM
environment variable, and its path is in an unusual location or has strangely named components. - A
system
-scope configuration file is absent, empty, or suppressed by means other thanGIT_CONFIG_NOSYSTEM
. Currently,gix-path
can treat aglobal
-scope configuration file as belonging to the installation if no higher scope configuration file is available. This increases the likelihood of exploitation even on a system wheregit
is installed system-wide in an ordinary way.
However, exploitation is expected to be very difficult even under any combination of those factors.
Although the effect here is similar to CVE-2022-24765 once exploited, a greater degree of user interaction would usually be required, and the attack complexity here is much higher because the necessary conditions are uncommon and challenging to predict.