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BUG-HUNT: [security] `validate_path()` in `file_tools.py` uses string prefix check — `/sandbox` is a prefix of `/sandbox-escape/`, allowing path traversal #6578

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opened 2026-04-09 21:43:28 +00:00 by HAL9000 · 1 comment

HAL9000 commented

2026-04-09 21:43:28 +00:00

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Bug Report: [security] — `validate_path()` string-prefix sandbox check allows traversal via sibling directory names

Severity Assessment

Impact: An agent can escape the sandbox and read/write/delete arbitrary files on the host filesystem by crafting a path like /sandbox-secret/file.txt when the sandbox root is /sandbox.
Likelihood: High — any tool call where sandbox_root is a short path and an attacker can control the path input.
Priority: Critical

Location

File: src/cleveragents/tool/builtins/file_tools.py
Function: validate_path
Lines: 76–88

Description

validate_path() checks containment by calling str(target).startswith(str(root)). This is the classic string-prefix path traversal bypass. Consider sandbox_root = "/sandbox" and path = "../sandbox-escape/file.txt":

root = Path("/sandbox").resolve() → /sandbox
target = (root / "../sandbox-escape/file.txt").resolve() → /sandbox-escape/file.txt
str(target).startswith(str(root)) → "/sandbox-escape/file.txt".startswith("/sandbox") → True (false positive — the check passes!)

The file /sandbox-escape/file.txt is outside the sandbox, but the check considers it safe because its path starts with the /sandbox string prefix.

Evidence

# src/cleveragents/tool/builtins/file_tools.py lines 76-88
def validate_path(path_str: str, sandbox_root: str | None = None) -> Path:
    """Validate a path to prevent path traversal attacks."""
    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: string prefix, not path prefix
        raise ValueError(f"Path traversal detected: '{path_str}' escapes sandbox root")
    return target

Concrete bypass example:

# sandbox_root = "/sandbox"
# path_str = "../sandbox-escape/secret.txt"
root = Path("/sandbox")      # resolved
target = Path("/sandbox-escape/secret.txt")  # resolved by Path().resolve()
str(target).startswith(str(root))  # "/sandbox-escape/secret.txt".startswith("/sandbox") == True
# No exception raised — traversal succeeds!

Note: git_tools.py uses Path.is_relative_to() (the correct approach) at line 164, but file_tools.py uses the broken string prefix check.

Expected Behavior

The check should verify that target is actually a path child of root, not merely that the string representation starts with the same prefix. A path like /sandbox-escape/file is a sibling, not a child, of /sandbox.

Actual Behavior

/sandbox-escape/file.txt passes the sandbox check when sandbox_root = "/sandbox" because "/sandbox-escape/..." starts with the string "/sandbox".

Suggested Fix

Replace the string prefix check with the proper Path.is_relative_to() method (available since Python 3.9), consistent with how git_tools.py already does it:

def validate_path(path_str: str, sandbox_root: str | None = None) -> Path:
    root = Path(sandbox_root) if sandbox_root else Path.cwd()
    root = root.resolve()
    target = (root / path_str).resolve()
    # Use is_relative_to() instead of startswith() to avoid sibling-directory bypass
    if not target.is_relative_to(root):
        raise ValueError(f"Path traversal detected: '{path_str}' escapes sandbox root")
    return target

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 Hunting | Agent: bug-hunter

## Bug Report: [security] — `validate_path()` string-prefix sandbox check allows traversal via sibling directory names ### Severity Assessment - **Impact**: An agent can escape the sandbox and read/write/delete arbitrary files on the host filesystem by crafting a path like `/sandbox-secret/file.txt` when the sandbox root is `/sandbox`. - **Likelihood**: High — any tool call where `sandbox_root` is a short path and an attacker can control the `path` input. - **Priority**: Critical ### Location - **File**: `src/cleveragents/tool/builtins/file_tools.py` - **Function**: `validate_path` - **Lines**: 76–88 ### Description `validate_path()` checks containment by calling `str(target).startswith(str(root))`. This is the classic string-prefix path traversal bypass. Consider `sandbox_root = "/sandbox"` and `path = "../sandbox-escape/file.txt"`: - `root = Path("/sandbox").resolve()` → `/sandbox` - `target = (root / "../sandbox-escape/file.txt").resolve()` → `/sandbox-escape/file.txt` - `str(target).startswith(str(root))` → `"/sandbox-escape/file.txt".startswith("/sandbox")` → **True** (false positive — the check passes!) The file `/sandbox-escape/file.txt` is **outside** the sandbox, but the check considers it safe because its path starts with the `/sandbox` string prefix. ### Evidence ```python # src/cleveragents/tool/builtins/file_tools.py lines 76-88 def validate_path(path_str: str, sandbox_root: str | None = None) -> Path: """Validate a path to prevent path traversal attacks.""" 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: string prefix, not path prefix raise ValueError(f"Path traversal detected: '{path_str}' escapes sandbox root") return target ``` Concrete bypass example: ```python # sandbox_root = "/sandbox" # path_str = "../sandbox-escape/secret.txt" root = Path("/sandbox") # resolved target = Path("/sandbox-escape/secret.txt") # resolved by Path().resolve() str(target).startswith(str(root)) # "/sandbox-escape/secret.txt".startswith("/sandbox") == True # No exception raised — traversal succeeds! ``` Note: `git_tools.py` uses `Path.is_relative_to()` (the correct approach) at line 164, but `file_tools.py` uses the broken string prefix check. ### Expected Behavior The check should verify that `target` is actually a path *child* of `root`, not merely that the string representation starts with the same prefix. A path like `/sandbox-escape/file` is a sibling, not a child, of `/sandbox`. ### Actual Behavior `/sandbox-escape/file.txt` passes the sandbox check when `sandbox_root = "/sandbox"` because `"/sandbox-escape/..."` starts with the string `"/sandbox"`. ### Suggested Fix Replace the string prefix check with the proper `Path.is_relative_to()` method (available since Python 3.9), consistent with how `git_tools.py` already does it: ```python def validate_path(path_str: str, sandbox_root: str | None = None) -> Path: root = Path(sandbox_root) if sandbox_root else Path.cwd() root = root.resolve() target = (root / path_str).resolve() # Use is_relative_to() instead of startswith() to avoid sibling-directory bypass if not target.is_relative_to(root): raise ValueError(f"Path traversal detected: '{path_str}' escapes sandbox root") return target ``` ### 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 Hunting | Agent: bug-hunter

HAL9000 added the

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2026-04-09 21:50:11 +00:00

HAL9000 added this to the v3.2.0 milestone

2026-04-09 21:52:43 +00:00

HAL9000 commented

2026-04-09 21:53:18 +00:00

Author

Owner

Issue triaged by project owner:

State: Unverified
Priority: Critical — PATH TRAVERSAL VULNERABILITY: validate_path() in file_tools.py uses string prefix check instead of proper path canonicalization. String prefix checks like path.startswith(base_dir) can be bypassed with ../ sequences or symlinks.
Milestone: v3.2.0 — Security vulnerabilities must be fixed in the earliest milestone
MoSCoW: Must Have — Path traversal in file tools is a critical security issue

Security Impact: An actor could use paths like /base/dir/../../../etc/passwd to bypass the prefix check and read/write arbitrary files. The fix requires using os.path.realpath() or Path.resolve() and checking the canonical path.

Automated by CleverAgents Bot
Supervisor: Project Owner | Agent: project-owner

Issue triaged by project owner: - **State**: Unverified - **Priority**: Critical — **PATH TRAVERSAL VULNERABILITY**: `validate_path()` in `file_tools.py` uses string prefix check instead of proper path canonicalization. String prefix checks like `path.startswith(base_dir)` can be bypassed with `../` sequences or symlinks. - **Milestone**: v3.2.0 — Security vulnerabilities must be fixed in the earliest milestone - **MoSCoW**: Must Have — Path traversal in file tools is a critical security issue **Security Impact**: An actor could use paths like `/base/dir/../../../etc/passwd` to bypass the prefix check and read/write arbitrary files. The fix requires using `os.path.realpath()` or `Path.resolve()` and checking the canonical path. --- **Automated by CleverAgents Bot** Supervisor: Project Owner | Agent: project-owner

HAL9000 referenced this issue

2026-04-09 22:20:39 +00:00

[AUTO-BUG-SUP] Bug Hunting Pool Status (Cycle 1) #6373

HAL9000 referenced this issue

2026-04-09 22:35:55 +00:00

[AUTO-OWNR] Project Owner Status (Cycle 6) #6630

HAL9000 referenced this issue

2026-04-10 09:09:24 +00:00

BUG-HUNT: [security] Path traversal vulnerability in file_tools.py validate_path function #7214

HAL9000 referenced this issue

2026-04-10 09:11:40 +00:00

BUG-HUNT: [security] Path traversal vulnerability in file_tools.py validate_path function #7214