@matheusbsbs / matheus-bagliano / commits / 20f3588efc

core.hooksPath: add some protection while cloning

Quite frequently, when vulnerabilities were found in Git's (quite complex) clone machinery, a relatively common way to escalate the severity was to trick Git into running a hook which is actually a script that has just been laid on disk as part of that clone. This constitutes a Remote Code Execution vulnerability, the highest severity observed in Git's vulnerabilities so far. Some previously-fixed vulnerabilities allowed malicious repositories to be crafted such that Git would check out files not in the worktree, but in, say, a submodule's `<git>/hooks/` directory. A vulnerability that "merely" allows to modify the Git config would allow a related attack vector, to manipulate Git into looking in the worktree for hooks, e.g. redirecting the location where Git looks for hooks, via setting `core.hooksPath` (which would be classified as CWE-427: Uncontrolled Search Path Element and CWE-114: Process Control, for more details see https://cwe.mitre.org/data/definitions/427.html and https://cwe.mitre.org/data/definitions/114.html). To prevent that attack vector, let's error out and complain loudly if an active `core.hooksPath` configuration is seen in the repository-local Git config during a `git clone`. There is one caveat: This changes Git's behavior in a slightly backwards-incompatible manner. While it is probably a rare scenario (if it exists at all) to configure `core.hooksPath` via a config in the Git templates, it _is_ conceivable that some valid setup requires this to work. In the hopefully very unlikely case that a user runs into this, there is an escape hatch: set the `GIT_CLONE_PROTECTION_ACTIVE=false` environment variable. Obviously, this should be done only with utmost caution. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Johannes Schindelin committed Mar 30, 2024 at 19:12 UTC 20f3588efc6cbcae5bbaabf65ee12df87b51a9ea

2 files changed +27 -1

config.c

+12 -1

@@ -1525,8 +1525,19 @@ static int git_default_core_config(const char *var, const char *value, void *cb)

1525 if (!strcmp(var, "core.attributesfile"))

1526 return git_config_pathname(&git_attributes_file, var, value);

1527

1528 - if (!strcmp(var, "core.hookspath"))

1528 + if (!strcmp(var, "core.hookspath")) {

1529 + if (current_config_scope() == CONFIG_SCOPE_LOCAL &&

1530 + git_env_bool("GIT_CLONE_PROTECTION_ACTIVE", 0))

1531 + die(_("active `core.hooksPath` found in the local "

1532 + "repository config:\n\t%s\nFor security "

1533 + "reasons, this is disallowed by default.\nIf "

1534 + "this is intentional and the hook should "

1535 + "actually be run, please\nrun the command "

1536 + "again with "

1537 + "`GIT_CLONE_PROTECTION_ACTIVE=false`"),

1538 + value);

1539 return git_config_pathname(&git_hooks_path, var, value);

1540 + }

1541

1542 if (!strcmp(var, "core.bare")) {

1543 is_bare_repository_cfg = git_config_bool(var, value);

t/t1800-hook.sh

+15

@@ -177,4 +177,19 @@ test_expect_success 'git hook run a hook with a bad shebang' '

177 test_cmp expect actual

178 '

179

180 +test_expect_success 'clone protections' '

181 + test_config core.hooksPath "$(pwd)/my-hooks" &&

182 + mkdir -p my-hooks &&

183 + write_script my-hooks/test-hook <<-\EOF &&

184 + echo Hook ran $1

185 + EOF

186 +

187 + git hook run test-hook 2>err &&

188 + grep "Hook ran" err &&

189 + test_must_fail env GIT_CLONE_PROTECTION_ACTIVE=true \

190 + git hook run test-hook 2>err &&

191 + grep "active .core.hooksPath" err &&

192 + ! grep "Hook ran" err

193 +'

194 +

195 test_done