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skillctl: Path traversal and symlink-follow in skillctl allow arbitrary file disclosure and deletion

High severity GitHub Reviewed Published May 20, 2026 in umanio-agency/skillctl • Updated Jun 5, 2026

Package

cargo skillctl (Rust)

Affected versions

< 0.1.2

Patched versions

0.1.2

Description

Impact

skillctl 0.1.0 and 0.1.1 contained four path-safety vulnerabilities that, in combination, allowed an attacker to:

  1. Exfiltrate arbitrary files on the operator's machine by publishing a malicious skills library containing a symlink inside a skill folder (e.g. niania → /home/user/.aws/credentials). The symlink fell through entry.file_type().is_dir() in fs_util::copy_dir_all, was dereferenced by fs::copy, and the target's content was copied into the project. A subsequent skillctl push would have published the secret to the (possibly public) library — what the reporter called "round-trip path exfiltration".

  2. Delete arbitrary directories outside the project or library root by crafting a .skills.toml with a malicious destination or source_path field. Both were deserialized as PathBuf with zero validation. Because Path::join lets an absolute right-hand side replace the base, destination = "/home/user/.ssh" made cwd.join(...) resolve outside the project; .. traversal was equally unguarded. Downstream remove_dir_all in replace_folder_contents then wiped arbitrary writable directories on skillctl pull / push / detect. .skills.toml is the exact kind of file teams commit and exchange via PR; a single merged malicious PR was sufficient to weaponise the maintainer's next skillctl pull --all.

  3. detect --target accepted .. traversal, even though absolute paths were rejected. --target ../../../etc would have written outside the library root.

  4. Fork-name validation accepted . and .. literally, so a fork named .. would have produced a Path::join resolving to the parent directory and fs::rename could have clobbered it.

Patches

Fixed in v0.1.2:

  • Symlinks inside skill folders are hard-rejected at copy time (both top-level source and any descendant entry).
  • .skills.toml destination and source_path are validated at load time and reject absolute paths, .. components, and Windows-prefix components.
  • A new path_safety::safe_join helper is wired (defense-in-depth) at every destructive call site in pull.rs / push.rs.
  • detect --target and the interactive custom-path prompt go through the same validate_relative_subpath helper.
  • validate_fork_name explicitly rejects . and ...

Threat-model note: the fix is purely lexical (component-level) plus an explicit symlink check at copy time. No filesystem canonicalize calls were added, avoiding TOCTOU windows.

Credit

Reported privately on 2026-05-19 by firebaguette via the Umanio Discord (the reporter declined GitHub credit, so this advisory carries no structured credits field).

References

@umanio-agency umanio-agency published to umanio-agency/skillctl May 20, 2026
Published to the GitHub Advisory Database Jun 5, 2026
Reviewed Jun 5, 2026
Last updated Jun 5, 2026

Severity

High

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 Network
Attack Complexity Low
Attack Requirements None
Privileges Required None
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality High
Integrity None
Availability Low
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:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N

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.

UNIX Symbolic Link (Symlink) Following

The product, when opening a file or directory, does not sufficiently account for when the file is a symbolic link that resolves to a target outside of the intended control sphere. This could allow an attacker to cause the product to operate on unauthorized files. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-wx3m-whqv-xv47

Source code

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