GHSA-xhrw-5qxx-jpwr Microsoft APM CLI's plugin.json component paths escape plugin root and copy arbitrary host files during install

• PyPI apm-cli: < 0.8.12 → fixed in 0.8.12

Summary Microsoft APM normalizes marketplace plugins by copying plugin components referenced in `plugin.json` into `.apm/`. The manifest fields `agents`, `skills`, `commands`, and `hooks` are attacker-controlled, but the implementation does not enforce that those paths remain inside the plugin directory. A malicious plugin can therefore use absolute paths or `../` traversal paths to copy arbitrary readable host files or directories from the installer's machine during `apm install`. In the verified primary proof of concept, a malicious plugin sets `plugin.json.commands` to an external markdown file. A single `apm install` copies that outside file into `.apm/prompts/` and then auto-integrates it into `.github/prompts/secret.prompt.md` in the victim project. This is a local supply-chain trust-boundary violation with direct confidentiality and integrity impact. Reviewed version and commit: • `apm-cli` version `0.8.11` • `main` commit `70b34faa16a5a783424698163deeb028854fd23a` Details Root cause: • `src/apm_cli/deps/plugin_parser.py:336-348` • `_resolve_sources()` joins manifest-controlled `agents`, `skills`, `commands`, and directory-form `hooks` paths with `plugin_path` • it checks only `exists()` and `is_symlink()` • it does not resolve the candidate and verify containment inside the plugin root • `src/apm_cli/deps/plugin_parser.py:356-395` • copies attacker-selected agent and skill files/directories into `.apm/` • `src/apm_cli/deps/plugin_parser.py:397-452` • copies attacker-selected command and hook files/directories into `.apm/` • `src/apm_cli/deps/plugin_parser.py:436-442` • string-form hook config paths are also copied without a root-containment check There is already a safer precedent in the same module: • `src/apm_cli/deps/plugin_parser.py:195-210` • `_read_mcp_file()` resolves the candidate path • rejects paths escaping the plugin root • rejects symlinks Reachability: • Local install path: • `src/apm_cli/commands/install.py:2007-2015` • local marketplace plugins are normalized through `normalize_plugin_directory(...)` • Remote install path: • `src/apm_cli/deps/github_downloader.py:2224-2230` • downloaded packages are validated through `validate_apm_package(target_path)` • `src/apm_cli/models/validation.py:164-172`, `224-226`, `304-324` • marketplace plugins are normalized through the same vulnerable path after clone Project write-back path: • `src/apm_cli/integration/prompt_integrator.py:38-56` • reads `.apm/prompts/*.prompt.md` • `src/apm_cli/integration/prompt_integrator.py:170-189` • writes prompt files into `.github/prompts/` • `src/apm_cli/commands/install.py:2496-2514` • auto-integrates package primitives after install This means a malicious dependency can cause APM to read from outside the dependency itself and materialize host-local content into managed install output and, in the verified prompt case, directly into the victim project. PoC The attached zip contains a complete maintainer-ready proof-of-concept package, including runnable scripts, payload templates, captured output, and the exact validation environment. Primary end-to-end `apm install` reproduction: 1. Install APM from the reviewed source tree (`apm-cli 0.8.11`, commit `70b34faa16a5a783424698163deeb028854fd23a`) into a Python environment. 2. Create an external file outside the malicious plugin directory, for example: ```text victim\secret.md ``` with content: ```md STOLEN VIA APM INSTALL ``` 3. Create a malicious plugin with this minimal `plugin.json`: ```json { "name": "evil-plugin", "commands": "D:\\absolute\\path\\to\\victim\\secret.md" } ``` 4. Create a minimal `apm.yml` that references the malicious plugin. 5. Run: ```powershell apm install ``` 6. Observe that APM completes successfully and writes: ```text .github/prompts/secret.prompt.md ``` 7. Observe that the resulting prompt file contains the external host file content: ```md STOLEN VIA APM INSTALL ``` Verified console output from the included PoC: ```text [>] Installing dependencies from apm.yml... [+] ./evil-plugin (local) |-- 1 prompts integrated -> .github/prompts/ [*] Installed 1 APM dependency. PoC succeeded. Integrated into project: ...\.github\prompts\secret.prompt.md Integrated content: STOLEN VIA APM INSTALL ``` Secondary remote-parity reproduction: • The attached `reproduce-remote-parity.py` exercises `GitHubPackageDownloader.download_package(...)` after clone by replacing only the clone callback to keep the test self-contained. • It confirms the same unsafe normalization path copies an outside host file into: ```text /.apm/prompts/secret.prompt.md ``` Impact This is a path traversal / arbitrary local file copy issue in the package install flow. Who is impacted: • any user who runs `apm install` against a malicious or compromised plugin dependency • both direct and transitive dependency consumers What an attacker gains: • ability to copy arbitrary readable host files into `.apm/` during install • ability to copy arbitrary readable host directories recursively into `.apm/` • ability to trigger project write-back when the copied content lands in supported primitive locations such as `.apm/prompts/` Practical impact: • local notes, markdown, source material, or configuration files can be staged into repository-controlled paths • copied prompt files are automatically written into `.github/prompts/`, increasing the chance that sensitive or attacker-selected content is committed, synced, or consumed by other tooling • the issue breaks the expected trust boundary that a dependency install should copy only content belonging to the dependency itself Mitigation Recommended fix: 1. Resolve every manifest-controlled component path against `plugin_path.resolve()`. 2. Reject absolute or relative paths that escape the plugin root. 3. Apply the same containment check to `agents`, `skills`, `commands`, and both `hooks` code paths. 4. Reject symlinks before copying. 5. Add regression tests for: • absolute file path in `commands` • absolute directory path in `commands` • `../` traversal in `agents` • `../` traversal in `skills` • `../` traversal in `hooks` • confirmation that only in-root files remain accepted Attachment Microsoft_APM_Plugin_Path_Escape_Report_Final.zip