fix(security): fix file_tools.py validate_path startswith bypass #7478

- Add CHANGELOG.md Security section entry for validate_path path traversal fix.
- Update CONTRIBUTORS.md with HAL 9000 contribution description.
- Fix BDD test scenario tag from @tdd_issue_7558 to @tdd_issue_7478.

ISSUES CLOSED: #7478

CHANGELOG.md

@@ -96,6 +96,18 @@ The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 ### Security
 
+- **file_tools.py `validate_path` startswith bypass** (#7478): Replaced the insecure
+  `str(target).startswith(str(root))` prefix check in
+  `cleveragents.tool.builtins.file_tools.validate_path()` with a proper
+  `Path.relative_to(root)` containment guard.  The old string-prefix approach was
+  vulnerable to a path-traversal bypass: a sandbox root of ``/tmp/sandbox`` combined
+  with a crafted path resolving to ``/tmp/sandbox-evil`` would incorrectly pass the
+  ``startswith`` check because the resolved target string literally begins with the
+  root string.  The new implementation uses Python's built-in ``Path.relative_to()``
+  which correctly rejects any target that is not *within* the sandbox directory
+  hierarchy, including the prefix-collision case where a sibling directory name
+  shadowed (i.e., was a string prefix of) the sandbox name.
+
 - **aiohttp upgraded to >=3.13.4 to remediate CVE-2026-34513 and CVE-2026-34515** (#1549, #1544):
   Added an explicit `aiohttp>=3.13.4` dependency constraint to `pyproject.toml` to remediate
   two high-severity open redirect vulnerabilities. Both CVEs affect the CleverAgents platform's

CONTRIBUTORS.md

@@ -19,6 +19,7 @@ Below are some of the specific details of various contributions.
 * HAL 9000 has contributed the plan concurrency race-condition fix (#7989): wired `LockService` into the plan lifecycle, guarding `execute_plan()` and `apply_plan()` with plan-level advisory locks and unique per-invocation owner identities to prevent silent concurrent state corruption.
 * HAL 9000 has contributed the bug-hunt-pool-supervisor non-blocking tracking fix: updated step 5 to be best-effort and added rule 9 to prevent the automation-tracking-manager call from blocking the main supervisor loop.
 * HAL 9000 has contributed the plugin entry point security hardening fix (#7476): enforced entry point allowlist validation before importing plugin modules to prevent malicious plugin loading.
+* HAL 9000 has contributed the `file_tools.py validate_path` path traversal startswith bypass fix (#7478): replaced the insecure `str(target).startswith(str(root))` prefix check with a proper `Path.relative_to(root)` containment guard to correctly reject sibling-directory prefix-collision escape paths.
 * HAL 9000 has contributed the benchmark workflow separation (#9040): moved the benchmark-regression job out of the default PR workflow into a dedicated scheduled workflow, reducing median PR CI turnaround time from 99-132 minutes to under 30 minutes.
 * HAL 9000 has contributed the agent-evolution-pool-supervisor PR metadata assignment (#7888): the supervisor now automatically looks up the Type/Automation label and earliest open milestone before dispatching improvement PR creation workers, ensuring all generated improvement PRs have correct Type labels and milestone assignments.
 * This project was made possible thanks to considerable donation of time, money, and resources by CleverThis, Inc.

features/tool_builtins.feature

@@ -160,7 +160,7 @@ Feature: Built-in File Tools
     Then the tool result should not be successful
     And the tool result error should mention "traversal"
 
-  @tdd_issue @tdd_issue_7558
+  @tdd_issue @tdd_issue_7478
   Scenario: Path traversal with sandbox name prefix collision is rejected
     Given a temporary sandbox directory
     And a sibling directory with a name that is a prefix of the sandbox name