CVE-2026-42574: Chainguard.dev/apko Path Traversal Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qq3r-w4hj-gjp6",
  "modified" : "2026-05-13T13:42:42Z",
  "published" : "2026-05-04T21:26:47Z",
  "aliases" : [ "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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "chainguard.dev/apko"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.14.8"
      }, {
        "fixed" : "1.2.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "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" : "WEB",
    "url" : "https://github.com/chainguard-dev/apko/pull/2187"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/chainguard-dev/apko/commit/f5a96e1299ac81c7ea9441705ec467688086f442"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/chainguard-dev/apko"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/chainguard-dev/apko/releases/tag/v1.2.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22", "CWE-59" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-04T21:26:47Z",
    "nvd_published_at" : "2026-05-09T20:16:29Z"
  }
}