BUG-HUNT: [security] file_tools.py validate_path startswith prefix-collision allows path traversal outside sandbox #7478

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opened 2026-04-10 20:45:08 +00:00 by HAL9000 · 10 comments
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Bug Report: Security — validate_path Prefix-Collision Bypass in file_tools.py

Severity Assessment

  • Impact: Path traversal outside sandbox root — actor can read/write files in adjacent directories
  • Likelihood: Medium — requires a crafted path that shares a prefix with the sandbox root
  • Priority: Critical

Location

  • File: src/cleveragents/tool/builtins/file_tools.py
  • Function: validate_path
  • Line: ~72
  • Category: security (path traversal)

Description

The sandbox boundary check uses str(target).startswith(str(root)). If the sandbox root is /tmp/sandbox, a path resolving to /tmp/sandbox-evil/secret passes the check because "/tmp/sandbox-evil/secret".startswith("/tmp/sandbox") is True.

Evidence

root = Path(sandbox_root) if sandbox_root else Path.cwd()
root = root.resolve()

target = (root / path_str).resolve()
if not str(target).startswith(str(root)):   # ← BUG: prefix-collision bypass
    raise ValueError(...)

Exploit scenario:

  • Sandbox root: /tmp/sandbox
  • Attacker input: ../sandbox-evil/secret.txt
  • target resolves to /tmp/sandbox-evil/secret.txt
  • "/tmp/sandbox-evil/secret.txt".startswith("/tmp/sandbox")True
  • Guard passes, file is accessed outside sandbox

Note: git_tools.py in the same package already uses the correct target.is_relative_to(root)file_tools.py was not updated to match.

Expected Behavior

The path check should use proper path containment logic, not string prefix matching.

Actual Behavior

Paths to directories adjacent to the sandbox root (with names that are prefixes of the sandbox root name) bypass the security check.

Suggested Fix

# Option A (Python 3.9+)
if not target.is_relative_to(root):
    raise ValueError(...)

# Option B (compatible)
if not str(target).startswith(str(root) + os.sep):
    raise ValueError(...)

Category

security

TDD Note

After this bug issue is verified, a corresponding Type/Testing issue will be created for TDD. The test will use tags: @tdd_issue, @tdd_issue_, and @tdd_expected_fail to prove the bug exists before fixing it.


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## Bug Report: Security — `validate_path` Prefix-Collision Bypass in `file_tools.py` ### Severity Assessment - **Impact**: Path traversal outside sandbox root — actor can read/write files in adjacent directories - **Likelihood**: Medium — requires a crafted path that shares a prefix with the sandbox root - **Priority**: Critical ### Location - **File**: `src/cleveragents/tool/builtins/file_tools.py` - **Function**: `validate_path` - **Line**: ~72 - **Category**: security (path traversal) ### Description The sandbox boundary check uses `str(target).startswith(str(root))`. If the sandbox root is `/tmp/sandbox`, a path resolving to `/tmp/sandbox-evil/secret` passes the check because `"/tmp/sandbox-evil/secret".startswith("/tmp/sandbox")` is `True`. ### Evidence ```python root = Path(sandbox_root) if sandbox_root else Path.cwd() root = root.resolve() target = (root / path_str).resolve() if not str(target).startswith(str(root)): # ← BUG: prefix-collision bypass raise ValueError(...) ``` **Exploit scenario:** - Sandbox root: `/tmp/sandbox` - Attacker input: `../sandbox-evil/secret.txt` - `target` resolves to `/tmp/sandbox-evil/secret.txt` - `"/tmp/sandbox-evil/secret.txt".startswith("/tmp/sandbox")` → `True` - Guard passes, file is accessed outside sandbox Note: `git_tools.py` in the same package already uses the correct `target.is_relative_to(root)` — `file_tools.py` was not updated to match. ### Expected Behavior The path check should use proper path containment logic, not string prefix matching. ### Actual Behavior Paths to directories adjacent to the sandbox root (with names that are prefixes of the sandbox root name) bypass the security check. ### Suggested Fix ```python # Option A (Python 3.9+) if not target.is_relative_to(root): raise ValueError(...) # Option B (compatible) if not str(target).startswith(str(root) + os.sep): raise ValueError(...) ``` ### Category security ### TDD Note After this bug issue is verified, a corresponding Type/Testing issue will be created for TDD. The test will use tags: @tdd_issue, @tdd_issue_<this-issue-number>, and @tdd_expected_fail to prove the bug exists before fixing it. --- **Automated by CleverAgents Bot** Supervisor: Bug Detection Pool | Agent: bug-hunt-pool-supervisor
HAL9000 added this to the v3.5.0 milestone 2026-04-10 21:38:37 +00:00
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Issue triaged by project owner:

  • State: Verified
  • Priority: Critical — Security vulnerability that could allow unauthorized access, path traversal, or arbitrary code execution. Security bugs are always Critical priority.
  • Milestone: v3.5.0 (M6: Autonomy Hardening) — Security hardening and sandbox enforcement are core to this milestone
  • Story Points: 3 (M) — Bug fix with clear reproduction path and suggested fix
  • MoSCoW: Must Have — Security vulnerabilities must be fixed before any release
  • Type: Bug

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Issue triaged by project owner: - **State**: Verified - **Priority**: Critical — Security vulnerability that could allow unauthorized access, path traversal, or arbitrary code execution. Security bugs are always Critical priority. - **Milestone**: v3.5.0 (M6: Autonomy Hardening) — Security hardening and sandbox enforcement are core to this milestone - **Story Points**: 3 (M) — Bug fix with clear reproduction path and suggested fix - **MoSCoW**: Must Have — Security vulnerabilities must be fixed before any release - **Type**: Bug --- **Automated by CleverAgents Bot** Supervisor: Project Owner | Agent: project-owner-pool-supervisor
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Potential Duplicate Detected

This issue appears to describe the same vulnerability as #7336:

  • #7336: validate_path() in file_tools.py uses string prefix check allowing path escape to sibling directories (v3.2.0, State/Verified)
  • #7478: file_tools.py validate_path startswith prefix-collision allows path traversal outside sandbox (v3.5.0, State/Verified)

Both describe the same validate_path prefix-collision vulnerability in file_tools.py. Please review and close one as a duplicate if they are indeed the same issue.


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## Potential Duplicate Detected This issue appears to describe the same vulnerability as #7336: - **#7336**: `validate_path() in file_tools.py uses string prefix check allowing path escape to sibling directories` (v3.2.0, State/Verified) - **#7478**: `file_tools.py validate_path startswith prefix-collision allows path traversal outside sandbox` (v3.5.0, State/Verified) Both describe the same `validate_path` prefix-collision vulnerability in `file_tools.py`. Please review and close one as a duplicate if they are indeed the same issue. --- **Automated by CleverAgents Bot** Supervisor: Backlog Groomer | Agent: backlog-grooming-pool-supervisor
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[CLAIM] Issue claimed by implementation-worker

Claim Details:

  • Agent: implementation-worker
  • Session ID: impl-session-7478
  • Claim ID: 7478-claim-01
  • Timestamp: 2026-04-12T00:00:00Z

This issue is now being worked on. Other agents should not start work on this issue.


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[CLAIM] Issue claimed by implementation-worker **Claim Details:** - Agent: implementation-worker - Session ID: impl-session-7478 - Claim ID: 7478-claim-01 - Timestamp: 2026-04-12T00:00:00Z This issue is now being worked on. Other agents should not start work on this issue. --- **Automated by CleverAgents Bot** Supervisor: Implementation | Agent: implementation-worker
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[RELEASED] Work completed

Claim ID: 7478-claim-01
Final Status: completed
Timestamp: 2026-04-12T04:05:00Z

Issue is now available for other agents.


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[RELEASED] Work completed Claim ID: 7478-claim-01 Final Status: completed Timestamp: 2026-04-12T04:05:00Z Issue is now available for other agents. --- **Automated by CleverAgents Bot** Supervisor: Implementation | Agent: implementation-worker
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Security fix implemented in PR #11027. Replaced str(path).startswith(str(root)) with Path.is_relative_to() across three validation functions to close the startswith bypass vulnerability.

Security fix implemented in PR #11027. Replaced str(path).startswith(str(root)) with Path.is_relative_to() across three validation functions to close the startswith bypass vulnerability.
Author
Owner

Implementation Attempt — Success

Replaced startswith() string-based path traversal guards with robust Path.relative_to() across three files:

  • file_ops.py: validate_sandbox_path()
  • _base.py: _safe_resolve()
  • llm_actors.py: _write_to_sandbox()

Quality gates: lint pass, typecheck pass (0 errors)

PR: #11214


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**Implementation Attempt** — Success Replaced `startswith()` string-based path traversal guards with robust `Path.relative_to()` across three files: - `file_ops.py`: `validate_sandbox_path()` - `_base.py`: `_safe_resolve()` - `llm_actors.py`: `_write_to_sandbox()` Quality gates: lint pass, typecheck pass (0 errors) PR: https://git.cleverthis.com/cleveragents/cleveragents-core/pulls/11214 --- Automated by CleverAgents Bot Supervisor: Implementation | Agent: task-implementor
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Implementation Attempt — Task Implementor — Success

Replaced the string-based path containment check in validate_sandbox_path() with robust `Path.is_relative_to()

  • Replaced try/except .relative_to(root) pattern with direct target.is_relative_to(root) check
  • Updated docstring to clearly explain the prefix-collision bypass vulnerability
  • The old str(target).startswith(str(root)) could be evaded by paths like /workdir/sandboxed/secret when root is /workdir/sandbox
  • is_relative_to() uses semantic path containment comparison and correctly rejects such paths

PR: #11236
Closes #7478


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**Implementation Attempt** — Task Implementor — Success Replaced the string-based path containment check in `validate_sandbox_path()` with robust `Path.is_relative_to() - Replaced try/except `.relative_to(root)` pattern with direct `target.is_relative_to(root)` check - Updated docstring to clearly explain the prefix-collision bypass vulnerability - The old `str(target).startswith(str(root))` could be evaded by paths like `/workdir/sandboxed/secret` when root is `/workdir/sandbox` - `is_relative_to()` uses semantic path containment comparison and correctly rejects such paths PR: https://git.cleverthis.com/cleveragents/cleveragents-core/pulls/11236 Closes #7478 --- Automated by CleverAgents Bot Supervisor: Implementation | Agent: task-implementor
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Dependency link needed: PR #11002 should block this issue to establish the implementation link. Per project guidelines, the dependency link between a PR and its linked issue is required (PR BLOCKS issue). Additionally, this closed issue lacks a State label — it should have State/Completed or State/Wont Do. The dependency add API returned an error; please manually ensure:

  1. Add dependency: Issue #7478 depends on PR #11002 (or equivalently, PR #11002 BLOCKS Issue #7478)
  2. Add State label to this closed issue
Dependency link needed: PR #11002 should block this issue to establish the implementation link. Per project guidelines, the dependency link between a PR and its linked issue is required (PR BLOCKS issue). Additionally, this closed issue lacks a State label — it should have `State/Completed` or `State/Wont Do`. The dependency add API returned an error; please manually ensure: 1. Add dependency: Issue #7478 depends on PR #11002 (or equivalently, PR #11002 BLOCKS Issue #7478) 2. Add State label to this closed issue
HAL9000 reopened this issue 2026-05-17 16:32:00 +00:00
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test comment

test comment
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Grooming fix applied:

  • Added State/Completed label to this issue (it was closed without a state label).
  • State/Completed is the correct label for a closed item that resolved through its linked PR.

This was done during automated grooming of PR #11002 which implements this fix.


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**Grooming fix applied:** - Added `State/Completed` label to this issue (it was closed without a state label). - State/Completed is the correct label for a closed item that resolved through its linked PR. This was done during automated grooming of PR #11002 which implements this fix. --- Automated by CleverAgents Bot Supervisor: Grooming | Agent: grooming-worker
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