Pin modules by Commit SHA

[timmeinerzhagen]

Current Terraform Version

v1.0.10

Problem

Git tags like v3.2.0 are mutable. This means a tag is not guaranteed to point to the same commit forever. Terraform adopts these tags for module versioning e.g. in the registry.

Some malicious party can easily delete a tag and create it again under the same name, just pointing to a new commit which includes their malicious content. Thus, everybody using this version is now using a malicious module.

Attempted Solutions

Using the Terraform Registry directly, only tags are allowed. An option is to reference the source GitHub Repository with the corresponding Commit Hash directly.

Example:

module "acm" {
  source = "github.com/terraform-aws-modules/terraform-aws-acm?ref=21d41965c40fbbb10710ab36404023e4379c7524"
  ...
}

This option however is not very readable and it would mean not using the Terraform Registry is the only safe option. Furthermore, any automatic version upgrade e.g. Dependabot have a harder time with this formatting.

Proposal

Giving the option to directly reference a commit via the Terraform registry reference would be ideal. See below.

module "acm" {
  source  = "terraform-aws-modules/acm/aws"
  version = "21d41965c40fbbb10710ab36404023e4379c7524" # v3.2.0
  ...
}

References

• GitHub: Guidance on pinning to Tag vs. Commit for GitHub Actions
• #4234
• Terraform Community: stale related discussion on Third-party Terraform module security/reproducibility

[crw]

Hi @timmeinerzhagen, thanks for your report! In terms of the behavior you are identifying, I verified with the Registry team that your assumptions are correct in terms of the direct link between registry version and source control, and the potential for the code referenced by a tag to change. I have filed an internal feature request issue with the Registry team.

[zwass]

FWIW with all the events of the last year (open source projects being replaced with malicious versions), this limitation makes the Terraform Registry unusable for our team.

[sobi3ch]

Hi @timmeinerzhagen, thanks for your report! In terms of the behavior you are identifying, I verified with the Registry team that your assumptions are correct in terms of the direct link between registry version and source control, and the potential for the code referenced by a tag to change. I have filed an internal feature request issue with the Registry team.

Hi @crw, I assume community cannot help with this internal request. Do you have any knowledge where we can see some results of Registry team work?

[crw]

Hi @sobi3ch, I do not. I have been checking in on it from time-to-time. The Registry team does not work out of this repository (they use an internal bug tracker) and typically I would close Registry issues here, however this issue seems interesting and important enough to keep a tracker open. If there is any update I'll be sure to let this thread know!

[jmgilman]

What's the priority on this? Given the recent attention the ESF has given to software supply chain security, this is a critical oversight by Hashicorp. Misformation about "pinning" using tags is opening up massive attack vectors for bad actors. Pinning by hash should be implemented as soon as possible and be the official recommended approach from Hashicorp for module consumers.

[fproulx-boostsecurity]

Any updates on this? Very concerned that we have lockfile just for providers..... Providers are much more mature and have tighter security on their codebase, generally, when you choose a module, you audit it, you'd hope you can pin it (for real, not just version tag).

[crw]

No updates. If you are a customer of Terraform Cloud or Terraform Enterprise, please file a ticket through the support channels: email [email protected] or open a new request. Thanks!

[opslivia]

This is not on the Registry's roadmap yet, but I will be moving this feature request into our internal backlog. @crw are you opposed to me closing it here?

[KyleKotowick]

I created a module that addresses this problem. It's an interim solution, but worth trying. Still experimental so feedback would be appreciated.

https://registry.terraform.io/modules/Invicton-Labs/module-lock/null/latest

[ThomasVanR]

This issue seems to be solved as explained in this comment: https://discuss.hashicorp.com/t/third-party-terraform-module-security-reproducibility/6995/8

[kmoe]

Modules are indeed pinned by commit SHA in the Terraform registry, mitigating the concern expressed in this issue.

As @apparentlymart says in the linked forum thread:

Today’s Terraform Registry now checks which commit the tag refers to at import time and then always returns that specific commit for any future request. Even if the tag in the repository changes to refer to a different commit later, the registry will continue returning the commit it originally discovered.

Note that the idea of client-side locking of modules by hash, such as is implemented by @KyleKotowick's module, is a separate feature and tracked by https://github.com/hashicorp/terraform/issues/17110.

[KyleKotowick]

@kmoe HashiCorp is missing a huge security vulnerability here. Module versions are pinned by commit SHA in the registry, but if the module author simply deletes a module version in the Registry and re-publishes it after moving the version tag in GitHub to a malicious commit, then once the CloudFront cache expires (7 days) it will start responding with the new (malicious) SHA hash, even though the same version number is being used.

I have sent complete reproducibility steps and a CVE ID request to [email protected].

[zwass]

If what @KyleKotowick is describing is true, that is very concerning. This issue should be reopened until that issue is remediated. @kmoe

[crw]

Thanks for this feedback. While we are still researching this new report, we continue to believe the correct solution will be in relation to https://github.com/hashicorp/terraform/issues/17110 -- so this issue will remain closed for the previously stated reasons. Thanks!

[github-actions[bot]]

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