## Summary
validatePath() in McpContext returned immediately, with no restriction
at all, whenever roots() returned undefined. roots() only returns
undefined when the connecting MCP client never negotiates the optional
roots capability during initialize, which any minimal client can trigger
simply by omitting it from its declared capabilities.
Since roots() already always appends the OS temp directory to whatever
explicit roots are configured, this change makes it return that same
default (temp directory only) instead of undefined when no roots have
been set. This removes the early return in validatePath() entirely, so
path validation now runs unconditionally rather than being conditional
on whether the connecting client happened to negotiate a capability it
was never required to declare per the MCP spec.
Any filePath-accepting tool (take_screenshot, saveFile, and the
performance/Lighthouse export tools that route through the same check)
had its only path-traversal guard silently disabled for the lifetime of
a connection whenever the client omitted the optional roots capability.
Since this server is designed to let an LLM drive a browser, and browsed
page content is not trusted input, this meant a client that simply
doesn't implement roots (a plausible, non-adversarial default for
lightweight or custom MCP clients) removed the only boundary preventing
the connected agent from writing to any path the process can reach.
Added a test that exercises the actual default state of roots (never
calling setRoots()) directly, since the existing tests always call
setRoots(), even with an empty array, before validating. Verified
locally with a minimal MCP client that declares no capabilities: before
this change, take_screenshot with a filePath outside any root wrote a
real file to an arbitrary path with no error; after this change, the
same call is rejected with the existing Access denied error. Also
verified that a client that does declare roots is unaffected, and that
writes to the OS temp directory continue to succeed with no roots
negotiated, matching prior behavior for that path.
Fixes output path validation so tools cannot validate one path and then
write to a different canonical target after extension enforcement.
Changes:
- Resolve dangling symlinks to their target path during
canonicalization.
- Validate the final extension-enforced output path before writing.
- Apply the same final-path validation to heap snapshots and
screencasts.
- Add regression coverage for dangling symlinks that point outside
configured roots.
Validation:
- npm run format
- npm run check-format
- npm run test tests/utils/files.test.ts
- npm run test tests/roots.test.ts
- npm run test tests/tools/memory.test.ts tests/tools/screencast.test.ts
Note: I also ran the full npm test suite locally. The targeted tests
above passed, but the full suite hit local WSL daemon/e2e startup
timeouts while waiting for daemon.pid / server_start, which appear
unrelated to this path-validation change.
---------
Co-authored-by: huynhtrungcsc <huynhtrungcsc@users.noreply.github.com>
This PR changes the implementation to allow access to tmpdir even if the
client is not configured it explicitly because several tools default to
the tmpdir for outputs. Many clients like gemini-cli/claude do not
configure the tmp dir as a root by default.
herdiyanitdev