{"id":"CVE-2026-42574","aliases":["GHSA-qq3r-w4hj-gjp6","GO-2026-5589"],"url":"https://o3.security/vulnerability/CVE-2026-42574","summary":"apko dirFS has a symlink-following path traversal that allows multiple entry points to escape the build root","details":"### Impact\n\nA 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.\n\n### Patches\n\nFixed in apko **v1.2.5** by [#2187](https://github.com/chainguard-dev/apko/pull/2187) / commit [f5a96e1](https://github.com/chainguard-dev/apko/commit/f5a96e1299ac81c7ea9441705ec467688086f442), 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.\n\n### Workarounds\n\nNo 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.\n\n### Resources\n\n- https://github.com/chainguard-dev/apko/pull/2187\n- https://github.com/chainguard-dev/apko/commit/f5a96e1299ac81c7ea9441705ec467688086f442\n- https://github.com/chainguard-dev/apko/releases/tag/v1.2.5\n- Related: GHSA-5g94-c2wx-8pxw (CVE-2026-25121) — prior lexical `..` traversal fix\n\n### Credits\n\napko thanks Oleh Konko ([@1seal](https://github.com/1seal) from [1seal.org](https://1seal.org/)) for the initial report of the symlink-escape class, and to [@Xh081iX](https://github.com/Xh081iX) for a follow-up set of reports covering additional reachable primitives (`ReadFile`, `Chmod`/`Chown`, `Mknod`, `MkdirAll`/`Mkdir`) that shaped the comprehensive fix.","published":"2026-05-09T19:24:48.497Z","modified":"2026-08-12T03:51:16.185667356Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"},"epss":{"score":0.00352,"percentile":0.27822,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"chainguard.dev/apko","fixedVersion":"1.2.5"}],"fix":{"url":"https://github.com/chainguard-dev/apko/commit/f5a96e1299ac81c7ea9441705ec467688086f442","label":"chainguard-dev/apko@f5a96e1"},"references":[{"type":"WEB","url":"https://github.com/chainguard-dev/apko/releases/tag/v1.2.5"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/42xxx/CVE-2026-42574.json"},{"type":"ADVISORY","url":"https://github.com/chainguard-dev/apko/security/advisories/GHSA-qq3r-w4hj-gjp6"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42574"},{"type":"FIX","url":"https://github.com/chainguard-dev/apko/commit/f5a96e1299ac81c7ea9441705ec467688086f442"},{"type":"FIX","url":"https://github.com/chainguard-dev/apko/pull/2187"},{"type":"PACKAGE","url":"https://github.com/chainguard-dev/apko"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:16.185667356Z"}}