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fix tar extraction add path validation to prevent escape from destination #4020

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fix tar extraction add path validation to prevent escape from destination #4020

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odaysec
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@odaysec odaysec commented Sep 29, 2025

Description

This fixes addresses path traversal vulnerabilities in tar archive extraction within the kind codebase. Without proper validation, specially crafted tar entries could escape the intended extraction directory and overwrite arbitrary files on the host system. This PR introduces safeguards to ensure that extracted files remain confined to the target directory.

kind/pkg/cluster/internal/logs/logs.go

Lines 77 to 97 in f20102c

abs := filepath.Join(dir, rel)
switch f.Typeflag {
case tar.TypeReg:
wf, err := os.OpenFile(abs, os.O_CREATE|os.O_RDWR, os.FileMode(f.Mode))
if err != nil {
return err
}
n, err := io.Copy(wf, tr)
if closeErr := wf.Close(); closeErr != nil && err == nil {
err = closeErr
}
if err != nil {
return errors.Errorf("error writing to %s: %v", abs, err)
}
if n != f.Size {
return errors.Errorf("only wrote %d bytes to %s; expected %d", n, abs, f.Size)
}
case tar.TypeDir:
if _, err := os.Stat(abs); err != nil {
if err := os.MkdirAll(abs, 0755); err != nil {

  • Issue: Tar archive entries are written to paths derived directly from the archive without validation. Attackers could craft entries with .. or absolute paths to escape the destination directory.

    • Compute the absolute path of the intended extraction target using filepath.Abs and filepath.Clean.
    • Verify that the target path begins with the cleaned absolute destination directory path.
    • Skip extraction (or return an error) for any entry that falls outside of the allowed directory.
    • Ensure this check is performed before any file system operations (e.g., os.Create, os.MkdirAll).

kind/pkg/build/nodeimage/internal/kube/tar.go

Lines 44 to 49 in f20102c

filepath.Join(destDirectory, filepath.Dir(hdr.Name)), os.FileMode(0o755),
); err != nil {
return fmt.Errorf("creating image directory structure: %w", err)
}
f, err := os.Create(filepath.Join(destDirectory, hdr.Name))

  • Issue: Similar to untar, the function does not validate hdr.Name, allowing malicious tar entries to escape the intended destination.
    • After joining hdr.Name with the target directory, normalize the path using filepath.Clean.
    • Confirm that the cleaned path remains within the cleaned target directory.
    • Reject or skip entries containing absolute paths or .. segments that lead outside the extraction directory.
    • Added a check using strings.HasPrefix(cleanedPath, cleanedDestDir + string(os.PathSeparator)) to enforce confinement.

Notes Refferences

  • No new dependencies were added; the fix leverages existing filepath, os, and strings packages.
  • The behavior of normal, well-formed tarballs remains unchanged.
  • Malicious or malformed entries are safely rejected.

@k8s-ci-robot k8s-ci-robot added the cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. label Sep 29, 2025
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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: odaysec
Once this PR has been reviewed and has the lgtm label, please assign aojea for approval. For more information see the Code Review Process.

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Welcome @odaysec!

It looks like this is your first PR to kubernetes-sigs/kind 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

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@k8s-ci-robot k8s-ci-robot added the needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. label Sep 29, 2025
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Hi @odaysec. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

@k8s-ci-robot k8s-ci-robot added the size/M Denotes a PR that changes 30-99 lines, ignoring generated files. label Sep 29, 2025
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odaysec commented Sep 29, 2025

/ok-to-test

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@odaysec: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

/ok-to-test

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

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Do you see a way where this is exposed in a way that could be exploited? Or was this just an AI recommendation?

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@aojea aojea Awaiting requested review from aojea

@BenTheElder BenTheElder Awaiting requested review from BenTheElder

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