ciguard: discover_pipeline_files follows symlinks out of scan root

Summary

The discover_pipeline_files() function in src/ciguard/discovery.py (introduced in v0.8.0 and used by the MCP scan_repo tool shipped in v0.8.1) walks a directory tree following symlinks, with cycle protection via tracking visited resolved paths. An attacker who can plant a symlink in a directory the user (or AI agent) scans can cause discovery to walk into the symlink target and return paths to pipeline-shaped files outside the requested root.

Threat scenario

MCP confused-deputy. A user runs Claude Desktop / Claude Code / Cursor with the ciguard MCP server registered. The agent is fed an adversarial prompt to scan a directory containing planted symlinks (e.g. via a malicious clone or extracted tarball). ciguard.scan_repo walks the symlinks, returning paths and (via subsequent scan calls) file content from ~/.aws/, ~/.config/, /etc/some-pipeline-config/, etc. Pipeline files often contain hardcoded secrets, internal hostnames, deploy keys.

Patch

• New follow_symlinks: bool = False parameter on discover_pipeline_files. Default refuses to descend into symlinked directories OR symlinked files.
• Belt-and-braces: results are filtered to those whose .resolve() lies under root.resolve(), applied even when callers opt in to follow_symlinks=True.
• 3 regression tests in tests/test_discovery.py::TestSymlinkSafety.

Discovery

Found during ciguard's first self-conducted penetration test cycle (PTES + OWASP TG v4.2 + CREST framing), 2026-04-26.

CVSS Scoring

• CVSS v3.1: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:L/I:N/A:N — 4.4 (Medium)
• CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:P/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N — first.org calc 5.7 (Medium); GitHub's calc returns 2.4 (Low). Vector is correct — calculator profiles differ.

Reproduction

from pathlib import Path
from ciguard.discovery import discover_pipeline_files
# In a victim dir, plant: trojan -> /etc
# (or any other accessible dir containing pipeline-shaped files)
for f in discover_pipeline_files(Path('/tmp/victim')):
    print(f)  # pre-fix: includes paths under /etc; post-fix: only /tmp/victim/

References

• Fix released in v0.8.2
• CI regression gate added in v0.8.3
• https://www.cve.org/CVERecord?id=CVE-2026-44220

See also: GHSA-w828-4qhx-vxx3 — same conceptual pattern (path-validation flaw in an AI-agent tool) in Claude SDK for Python, CWE-59 + CWE-367