Fix path traversal in GET /api/chat-modes/:modeId#44
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The modeId route parameter was joined into a filesystem path without validation. Express decodes URL-encoded characters in route params, so a request like GET /api/chat-modes/..%2F..%2Fsome-file would escape the prompts directory and read any .json file the backend process can access. Validate modeId against a strict allowlist regex before constructing the path; reject anything else with 400. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Summary
GET /api/chat-modes/:modeIdin backend/src/routes/chatModes.js joined themodeIdroute parameter directly into a filesystem path with no validation:Express decodes URL-encoded characters in route parameters, so a request like
GET /api/chat-modes/..%2F..%2Fsome-fileresolvesmodeIdto../../some-fileandpath.joinescapesPROMPTS_DIR. Any.jsonfile readable by the backend process could be disclosed through the response.Fix
Validate
modeIdagainst a strict allowlist regex (^[a-z0-9][a-z0-9-]{0,63}$) before constructing the path, and return400for anything else. The eight shipped mode ids (agent,planner,help-chat,brainstorm,discuss,edit,explore,generate) all match.Test plan
curl http://localhost:<port>/api/chat-modes/agent→ 200 with mode configcurl http://localhost:<port>/api/chat-modes/..%2F..%2Fpackage→ 400 (previously would attempt to readbackend/package.json)curl http://localhost:<port>/api/chat-modes/nonexistent→ 404curl http://localhost:<port>/api/chat-modes/UPPER→ 400