Summary
apko dirFS has a symlink-following path traversal that allows multiple entry points to escape the build root
Full technical description
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.
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.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-42574 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.2.5); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
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.
Frequently Asked Questions
- What is CVE-2026-42574? CVE-2026-42574 is a high-severity path traversal vulnerability in chainguard.dev/apko (go), affecting versions >= 0.14.8, < 1.2.5. It is fixed in 1.2.5. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-42574? CVE-2026-42574 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of chainguard.dev/apko are affected by CVE-2026-42574? chainguard.dev/apko (go) versions >= 0.14.8, < 1.2.5 is affected.
- Is there a fix for CVE-2026-42574? Yes. CVE-2026-42574 is fixed in 1.2.5. Upgrade to this version or later.
- Is CVE-2026-42574 exploitable, and should I be worried? Whether CVE-2026-42574 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-42574 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-42574? Upgrade
chainguard.dev/apkoto 1.2.5 or later.