GHSA-qq3r-w4hj-gjp6 apko dirFS has a symlink-following path traversal that allows multiple entry points to escape the build root

• Go chainguard.dev/apko: >= 0.14.8, < 1.2.5 → fixed in 1.2.5

Impact A crafted `.apk` could install a `TypeSymlink` tar entry whose target pointed outside the build root, and a subsequent directory-creation or file-write entry in the same or later archive could traverse that symlink to reach host paths the build user could write to. The root cause was the `sanitizePath` helper in `pkg/apk/fs/rwosfs.go`, which rejected only lexical `..` traversal and did not resolve or refuse symlinks. Every disk-backed `DirFS` method that handed its caller-supplied path to a symlink-following stdlib call — `ReadFile`, `WriteFile`, `Chmod`, `Chown`, `Chtimes`, `MkdirAll`, `Mkdir`, and `Mknod` — was affected. The reachable primitive from a malicious APK during tar extraction is the `MkdirAll` / `Mkdir` / `WriteFile` chain via `apko build-cpio` and disk-backed consumers such as `melange`; the remaining sinks are reachable by direct callers of the `pkg/apk/fs` package. The in-memory `tarfs` install path used by `apko build`, `apko publish`, and `apko build-minirootfs` is not affected. Patches Fixed in apko v1.2.5 by #2187 / commit f5a96e1, which scopes all `DirFS` operations through a Go 1.24 `*os.Root`. The `sanitizePath` helper has been removed; `*os.Root` refuses traversal via `..`, absolute-target symlinks, relative-target symlinks, and hardlinks by construction. Regression tests in `pkg/apk/apk/path_traversal_test.go` cover each composite primitive. Workarounds No complete workaround. Operators running pre-1.2.5 apko (or downstream tools such as melange that embed pre-1.2.5 `pkg/apk/fs`) should upgrade. Consuming only APKs from trusted, signed sources reduces but does not eliminate exposure. Resources • https://github.com/chainguard-dev/apko/pull/2187 • https://github.com/chainguard-dev/apko/commit/f5a96e1299ac81c7ea9441705ec467688086f442 • https://github.com/chainguard-dev/apko/releases/tag/v1.2.5 • Related: GHSA-5g94-c2wx-8pxw (CVE-2026-25121) — prior lexical `..` traversal fix Credits apko thanks Oleh Konko (@1seal from 1seal.org) for the initial report of the symlink-escape class, and to @Xh081iX for a follow-up set of reports covering additional reachable primitives (`ReadFile`, `Chmod`/`Chown`, `Mknod`, `MkdirAll`/`Mkdir`) that shaped the comprehensive fix.