GHSA-WX3M-WHQV-XV47

Vulnerability from github – Published: 2026-06-05 19:43 – Updated: 2026-06-05 19:46
VLAI
Summary
skillctl: Path traversal and symlink-follow in skillctl allow arbitrary file disclosure and deletion
Details

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).

Show details on source website

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "skillctl"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.1.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-22",
      "CWE-61"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-05T19:43:51Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Impact\n\n`skillctl` 0.1.0 and 0.1.1 contained four path-safety vulnerabilities that, in combination, allowed an attacker to:\n\n1. **Exfiltrate arbitrary files on the operator\u0027s machine** by publishing a malicious skills library containing a symlink inside a skill folder (e.g. `niania \u2192 /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\u0027s content was copied into the project. A subsequent `skillctl push` would have published the secret to the (possibly public) library \u2014 what the reporter called \"round-trip path exfiltration\".\n\n2. **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\u0027s next `skillctl pull --all`.\n\n3. **`detect --target` accepted `..` traversal**, even though absolute paths were rejected. `--target ../../../etc` would have written outside the library root.\n\n4. **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.\n\n## Patches\n\nFixed in [v0.1.2](https://github.com/umanio-agency/skillctl/releases/tag/v0.1.2):\n\n- Symlinks inside skill folders are hard-rejected at copy time (both top-level source and any descendant entry).\n- `.skills.toml` `destination` and `source_path` are validated at load time and reject absolute paths, `..` components, and Windows-prefix components.\n- A new `path_safety::safe_join` helper is wired (defense-in-depth) at every destructive call site in `pull.rs` / `push.rs`.\n- `detect --target` and the interactive custom-path prompt go through the same `validate_relative_subpath` helper.\n- `validate_fork_name` explicitly rejects `.` and `..`.\n\nThreat-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.\n\n## Credit\n\nReported privately on 2026-05-19 by **firebaguette** via the Umanio Discord (the reporter declined GitHub credit, so this advisory carries no structured credits field).",
  "id": "GHSA-wx3m-whqv-xv47",
  "modified": "2026-06-05T19:46:18Z",
  "published": "2026-06-05T19:43:51Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/umanio-agency/skillctl/security/advisories/GHSA-wx3m-whqv-xv47"
    },
    {
      "type": "WEB",
      "url": "https://github.com/umanio-agency/skillctl/commit/827fff5c0698dd9e48e777d5907cf7bc19b91aca"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/umanio-agency/skillctl"
    },
    {
      "type": "WEB",
      "url": "https://github.com/umanio-agency/skillctl/releases/tag/v0.1.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "skillctl: Path traversal and symlink-follow in skillctl allow arbitrary file disclosure and deletion"
}



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