fkie_cve-2026-123368

compose-lint is a Docker Compose security linter that identifies dangerous misconfigurations before deployment. From 0.22.0 until 0.31.0, compose-lint follows a sibling .env symbolic link outside the project without applying its normal containment check. From 0.28.0, the same gap also affects an include project_directory link outside the project. A pull request can reference a variable from the linked file, causing substitution to place runner file or process-environment data into finding messages written to logs, JSON, SARIF artifacts, and Code Scanning alerts. Reading /proc/self/environ can expose the remainder of the linter process environment because NUL-separated entries are treated as one value, although disclosure requires a workflow that processes untrusted changes with useful environment data and GitHub normally withholds secrets from fork pull requests. The pass or fail result is not changed. This issue is fixed in version 0.31.0.

GHSA-6wcv-rj3c-mhv3 — compose-lint: .env read through a symlink outside the project can expose the CI job's environment

Affected: PyPI: compose-lint, GitHub Actions: tmatens/compose-lint

### Impact

compose-lint fills in `${VAR}` references from the `.env` file next to the Compose file. It is meant to read nothing outside the project directory, and `env_file:`, `include:` and `extends:` paths are checked for that. The `.env` read is not. If `.env` is a symlink, compose-lint follows it wherever it points.

A pull request can add a `.env` symlink to any file on the CI runner and a Compose file that references a variable from it. compose-lint substitutes the value and quotes it in finding messages, which go to the log and to JSON and SARIF output.

The worst target is `/proc/self/environ`, the linter's own environment. The Compose file only needs to reference the name of the first variable in it: because that file separates variables with NUL bytes rather than newlines, the substituted value is the entire rest of the environment. On a CI runner that environment holds whatever the workflow put there, including secrets. GitHub masks registered secrets in the job log, but not in uploaded JSON or SARIF artifacts or in Code Scanning alert text.

An `include:` entry's `project_directory:` has the same gap from 0.28.0: a directory symlink named there makes compose-lint read `.env` from wherever the link points.

Pull requests from forks normally run without secrets, and GitHub masks registered secrets in the job log, so in the common setup what can be read is runner metadata and whatever unmasked values the job's environment holds. That is why this is scored as low co…

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fkie_cve-2026-123368

GHSA-6wcv-rj3c-mhv3 — compose-lint: .env read through a symlink outside the project can expose the CI job's environment