GHSA-whr6-fgpq-fpv9: compose-lint: A committed symlink makes compose-lint quote a file from outside the project into its output

Impact

Like Docker Compose, compose-lint follows symlinks when it reads a project's files. Unlike Compose, compose-lint up to 0.24.0 could then put the contents of a file from outside the project into its output, where the author of a pull request can read it.

A pull request can commit a symlink, under a name compose-lint reads, pointing at a file on the CI runner:

- The Compose file itself (0.2.0–0.24.0). A compose.yml that is a symlink, whether the pre-commit hook passes its name or the Action or a bare run finds it. - compose.override.yml (0.22.0–0.24.0), which compose-lint merges automatically. - A COMPOSEFILE entry (0.22.0–0.24.0) in a .env beside the Compose file.

When the target is not valid YAML, the parse error quotes the line it failed on. Docker Compose, given the same file, reports only a line number. That line reaches standard error (the job log), JSON errors[], and the SARIF toolExecutionNotifications, which the Action uploads to Code Scanning.

A fourth route: from 0.23.0, a symlinked envfile: target makes CL-0020 and CL-0021 report the credential-like key names in a file outside the project. Values are not printed.

What can be read is one line of a file chosen by path, at the point where the YAML parser fails, which the attacker cannot choose; or key names. A symlink to /proc/self/environ gave neither in testing. The pass/fail result is not affected. On a public repository the job log is visible to the pull request's author.

Found during an internal pre-1.0 security review.

GitHub Action. Action tags v0.18.0 through v0.24.0 install their own compose-lint version and are affected. Earlier tags install the newest release unless version: is set; they were affected while that was 0.24.0 or earlier.

Docker image. composelint/compose-lint tags 0.3.3 through 0.24.0, and the matching minor tags, are affected. Inside the container a symlink resolves within the container, so what can be read is the container's own files and anything mounted into it. Fixed from 0.25.0.

Patches

Fixed in 0.25.0. Parse errors no longer quote the source line; the error and its line and column are kept. envfile: targets and COMPOSEFILE entries that resolve outside the project are also refused, with the existing outside-the-project note. Symlinks that stay inside the project still work.

From 0.25.0 through 0.31.0, a committed symlink to a target that is itself a Compose file could still be read, and its values could reach findings. 0.32.0 stops following a discovered, named or override Compose file whose link leaves the checkout.

A related gap for the sibling .env file is covered by GHSA-6wcv-rj3c-mhv3, and one for a symlinked .compose-lint.yml by GHSA-88f4-frh5-gmcr.

Workarounds

- Upgrade to 0.25.0 or later. - On older versions, don't run compose-lint on untrusted pull requests on a machine whose files outside the checkout hold credentials. --no-env closes the COMPOSEFILE and envfile: routes, but not the others.

Reproduction

project/compose.yml -> /path/outside/project/credentials (symlink)

compose-lint --format sarif compose.yml on 0.24.0 exits 2, and the SARIF notification quotes a line of the linked file. On 0.25.0 the error gives only the line and column.