Terragrunt catalog predictable temp symlink clobber

Overview

Summary

Terragrunt's terragrunt catalog command clones each repository referenced in your catalog configuration into a temporary working directory. In affected versions, the clone path it derived was deterministic and sat under the shared system temporary directory, in the form <tmp>/catalog-<base64 sha1 of the repo URL>. Because that path was predictable and Terragrunt followed a symlink already present there instead of rejecting it, a local attacker could plant a symlink at that path and cause Terragrunt to delete a directory and re-clone into it outside the intended temporary root.

Impact

This affected users who ran terragrunt catalog on a host they shared with other local users or processes they did not fully trust, such as a multi-user server or a shared CI runner. The attack required a local attacker: a separate local user or process able to write to the shared system temporary directory. It was not remotely exploitable, and the victim had to run terragrunt catalog while the attacker's symlink was already in place.

Because the predictable path depended only on the repository URL being cataloged and the location of the system temporary directory, the attacker could compute it in advance and plant a symlink there before the victim ran the command. When the victim ran terragrunt catalog, Terragrunt followed the symlink out of the intended temporary root, deleted an existing <repoName> directory under the attacker-chosen parent, and repopulated that path with the cloned repository contents. All of this happened in the security context of the user running Terragrunt.

The attacker controlled the parent directory the symlink pointed to, but not the leaf name: the leaf was fixed to <repoName>, derived from the repository URL the victim cataloged. The primitive was deletion of an existing <repoName> directory outside the temporary root, followed by a re-clone into that same path. On a single-user machine with no hostile local processes, exposure was minimal.

Affected Versions

• Terragrunt < v1.1.1

Patches

This vulnerability has been resolved in Terragrunt version v1.1.1.

All users are strongly advised to upgrade.

Workarounds

If you cannot upgrade immediately, ensure that you do not allow untrusted parties to control the values of TMPDIR, TMP, and TEMP in environments where you run terragrunt catalog.

Technical Details

When you run terragrunt catalog, the catalog service iterates over the repositories in your configuration and prepares a local clone of each one. In affected versions, for a given repository URL it built a clone path by hashing the URL and joining the result under the shared system temporary directory:

<tmp>/catalog-<base64 sha1 of the repo URL>

This path was fully determined by the repository URL and the location of the system temporary directory, so anyone else on the machine who knew which repository a victim would catalog could compute it in advance. The catalog service passed this path into its clone preparation step.

As a result, an attacker who placed a symlink at <tmp>/catalog-<hash> pointing at a directory of their choosing caused both the removal and the re-clone to operate through that symlink. Both landed at <attacker-chosen-parent>/<repoName>, outside the intended temporary root.

Terragrunt v1.1.1 no longer derives a predictable clone path, so an attacker can no longer position a symlink at a location known in advance.

Credit

We would like to thank (@br0x2) for discovering and responsibly disclosing this vulnerability.

Affected packages

• github.com/gruntwork-io/terragrunt < 1.1.1

Remediation

Upgrade to a patched release:

• github.com/gruntwork-io/terragrunt 1.1.1