buildah/copier EUVD-2026-78823

Exploitation requires an application to use the buildah/copier Go package to extract a tar archive OUTSIDE of Buildah and as a non-root caller - Buildah's own extraction path uses chroot hardening and is explicitly NOT affected. The attacker must be able to supply a crafted tar archive containing malicious symlink entries to that extractor (UI:R - the victim application must actually process/extract the archive). Limiting factors: the flaw does not apply to Buildah/Podman default usage, impact is integrity-only (arbitrary file creation outside the destination, no data disclosure or DoS scored), and it is non-automatable per SSVC.

This is a genuinely moderate, not critical, issue and the signals are internally consistent in that direction. The vendor CVSS3.1 score is 4.5 (AV:N/AC:L/PR:H/UI:R/S:U/C:N/I:H/A:N) - integrity-only, no confidentiality or availability impact, and gated behind both high privileges and user interaction. EPSS is low at 0.25% (16th percentile), there is no CISA KEV listing, and no public exploit code has been identified. CISA SSVC reinforces low urgency: Exploitation=none, Automatable=no, Technical Impact=partial. All signals agree this is a low-priority, defense-in-depth fix rather than an emergency. One conflict worth flagging: the CVSS vector uses AV:N and PR:H, but the actual threat model is a library (buildah/copier) extracting an attacker-supplied tar - the attacker needs no privileges on the target host, while the running application (the victim) supplies/extracts the archive. That better matches PR:N/UI:R, which would raise the score; PR:H appears to reflect the narrow set of callers that invoke copier outside Buildah rather than an authentication requirement on the attacker. AV:N is defensible only if the malicious tar arrives over the network; for purely local archive processing AV:L is more accurate. The most important scoping fact is that Buildah itself is NOT affected (it uses chroot hardening) - only non-root code paths that call the copier package directly outside Buildah are vulnerable, which sharply limits real-world exposure.

An application that embeds the buildah/copier Go package (outside of Buildah, running as a non-root user) extracts a tar archive supplied by an attacker. The archive contains malicious symlink entries that redirect extraction outside the intended target directory, letting the attacker create or overwrite files at attacker-chosen paths with the privileges of the extracting process. No public exploit code has been identified, and CISA SSVC rates it non-automatable.