[GHSA] GHSA-mmg6-4qmv-6pc8 (medium) — Infracost: Arbitrary file read via config-template readFile symlink traversal

GHSA-mmg6-4qmv-6pc8 Severity: medium CVE: CVE-2026-71493

Infracost: Arbitrary file read via config-template readFile symlink traversal

### Impact

Path traversal via link following in the Infracost config-template parser. The `readFile`, `pathExists`, `isDir`, and `matchPaths` template functions confined repo-supplied paths with a lexical `filepath.Rel` check plus a leaf-only `os.Lstat`:

``` {{