runc: Malicious image with /dev symlink can trigger limited host filesystem integrity violations

runc is a CLI tool for spawning and running containers according to the OCI specification. In versions prior to 1.3.6, 1.4.0-rc.1, 1.4.0-rc.12, 1.5.0-rc.1, and 1.5.0-rc.1, when setting up the container rootfs, setupPtmx and setupDevSymlinks call os.Remove and os.Symlink with a filepath.Join string which allow an image with /dev as a symlink to trick runc into deleting files called ptmx on the host or creating a hardcoded set of symlinks with specific names and targets in an arbitrary pre-existing host directory. This issue is not exploitable under Docker, because Docker creates a top-level read-only layer that masks any malicious /dev symlink present in the container image — unlike some other Linux container tooling, whose higher-level runtimes built on runc remain exposed to exploitation via a malicious image. This issue has been fixed in versions 1.3.6, 1.4.3 and 1.5.0.

Source published

1 Jul 2026 00:02:08 UTC

Source modified

1 Jul 2026 13:35:41 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 3.3 CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N