🛡️ Sentinel: [CRITICAL] Fix TOCTOU vulnerability in JSON file adapters - #84
🛡️ Sentinel: [CRITICAL] Fix TOCTOU vulnerability in JSON file adapters#84ivangegovdve-sudo wants to merge 1 commit into
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Co-authored-by: ivangegovdve-sudo <225339531+ivangegovdve-sudo@users.noreply.github.com>
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Code Review
This pull request enhances security by mitigating TOCTOU vulnerabilities and OOM DoS risks in file-backed adapters through the implementation of bounded reads and explicit file type checks. The documentation was also updated to reflect these best practices. Review feedback suggests refining the technical language in the documentation and replacing repeated magic numbers with constants to improve maintainability.
| ## 2024-05-18 - [TOCTOU in file size limit checking] | ||
| **Vulnerability:** Checking file size using `path.stat().st_size` prior to reading is vulnerable to Time-Of-Check to Time-Of-Use (TOCTOU) and out-of-memory DoS, as well as bypassing checks via device files like `/dev/zero` which report size 0. | ||
| **Learning:** `path.exists()` or `path.stat().st_size` checks the state of the filesystem. By the time the file is read, the file could have been changed, or a different file type like a device file could have been placed there, evading the check. | ||
| **Prevention:** Verify it's a regular file first (`path.is_file()`), then read with a strict bound like `f.read(limit + 1)`, and if the read returned size is strictly greater than the limit, throw a size limit exception. |
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For improved clarity and technical accuracy, I suggest a small wording change in the prevention description. The read() method returns the file content (as a string or bytes), not its size. The check is performed on the length of this content.
| **Prevention:** Verify it's a regular file first (`path.is_file()`), then read with a strict bound like `f.read(limit + 1)`, and if the read returned size is strictly greater than the limit, throw a size limit exception. | |
| **Prevention:** Verify it's a regular file first (`path.is_file()`), then read with a strict bound like `f.read(limit + 1)`, and if the length of the content read is greater than the limit, throw a size limit exception. |
| with open(path, encoding="utf-8") as f: | ||
| content = f.read(10 * 1024 * 1024 + 1) | ||
| if len(content) > 10 * 1024 * 1024: | ||
| raise ValueError(f"Checkpoint file {path} exceeds 10MB size limit") |
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The file size limit 10 * 1024 * 1024 is repeated and is a 'magic number'. To improve readability and maintainability, it's best to define it as a constant. This makes the code easier to understand and safer to modify in the future.
Additionally, consider updating the hardcoded '10MB' in the error message to be derived from the constant to prevent inconsistencies if the limit changes.
| with open(path, encoding="utf-8") as f: | |
| content = f.read(10 * 1024 * 1024 + 1) | |
| if len(content) > 10 * 1024 * 1024: | |
| raise ValueError(f"Checkpoint file {path} exceeds 10MB size limit") | |
| _MAX_FILE_SIZE_BYTES = 10 * 1024 * 1024 | |
| with open(path, encoding="utf-8") as f: | |
| content = f.read(_MAX_FILE_SIZE_BYTES + 1) | |
| if len(content) > _MAX_FILE_SIZE_BYTES: | |
| raise ValueError(f"Checkpoint file {path} exceeds {_MAX_FILE_SIZE_BYTES // (1024*1024)}MB size limit") |
| # Security: Use bounded read (limit + 1) to prevent out-of-memory DoS | ||
| # from excessively large files or malicious device files (e.g., /dev/zero). | ||
| with open(self._file_path, encoding="utf-8") as f: | ||
| content = f.read(10 * 1024 * 1024 + 1) | ||
| if len(content) > 10 * 1024 * 1024: | ||
| raise ValueError( | ||
| f"Practice repository file {self._file_path} " | ||
| "exceeds 10MB size limit" | ||
| ) |
There was a problem hiding this comment.
The file size limit 10 * 1024 * 1024 is repeated and is a 'magic number'. To improve readability and maintainability, it's best to define it as a constant. This makes the code easier to understand and safer to modify in the future.
Additionally, consider updating the hardcoded '10MB' in the error message to be derived from the constant to prevent inconsistencies if the limit changes.
| # Security: Use bounded read (limit + 1) to prevent out-of-memory DoS | |
| # from excessively large files or malicious device files (e.g., /dev/zero). | |
| with open(self._file_path, encoding="utf-8") as f: | |
| content = f.read(10 * 1024 * 1024 + 1) | |
| if len(content) > 10 * 1024 * 1024: | |
| raise ValueError( | |
| f"Practice repository file {self._file_path} " | |
| "exceeds 10MB size limit" | |
| ) | |
| _MAX_FILE_SIZE_BYTES = 10 * 1024 * 1024 | |
| # Security: Use bounded read (limit + 1) to prevent out-of-memory DoS | |
| # from excessively large files or malicious device files (e.g., /dev/zero). | |
| with open(self._file_path, encoding="utf-8") as f: | |
| content = f.read(_MAX_FILE_SIZE_BYTES + 1) | |
| if len(content) > _MAX_FILE_SIZE_BYTES: | |
| raise ValueError( | |
| f"Practice repository file {self._file_path} " | |
| f"exceeds {_MAX_FILE_SIZE_BYTES // (1024*1024)}MB size limit" | |
| ) |
| # Security: Use bounded read (limit + 1) to prevent out-of-memory DoS | ||
| # from excessively large files or malicious device files (e.g., /dev/zero). | ||
| with open(self._file_path, encoding="utf-8") as f: | ||
| content = f.read(10 * 1024 * 1024 + 1) | ||
| if len(content) > 10 * 1024 * 1024: | ||
| raise ValueError( | ||
| f"Progress snapshot file {self._file_path} exceeds 10MB size limit" | ||
| ) |
There was a problem hiding this comment.
The file size limit 10 * 1024 * 1024 is repeated and is a 'magic number'. To improve readability and maintainability, it's best to define it as a constant. This makes the code easier to understand and safer to modify in the future.
Additionally, consider updating the hardcoded '10MB' in the error message to be derived from the constant to prevent inconsistencies if the limit changes.
| # Security: Use bounded read (limit + 1) to prevent out-of-memory DoS | |
| # from excessively large files or malicious device files (e.g., /dev/zero). | |
| with open(self._file_path, encoding="utf-8") as f: | |
| content = f.read(10 * 1024 * 1024 + 1) | |
| if len(content) > 10 * 1024 * 1024: | |
| raise ValueError( | |
| f"Progress snapshot file {self._file_path} exceeds 10MB size limit" | |
| ) | |
| _MAX_FILE_SIZE_BYTES = 10 * 1024 * 1024 | |
| # Security: Use bounded read (limit + 1) to prevent out-of-memory DoS | |
| # from excessively large files or malicious device files (e.g., /dev/zero). | |
| with open(self._file_path, encoding="utf-8") as f: | |
| content = f.read(_MAX_FILE_SIZE_BYTES + 1) | |
| if len(content) > _MAX_FILE_SIZE_BYTES: | |
| raise ValueError( | |
| f"Progress snapshot file {self._file_path} exceeds {_MAX_FILE_SIZE_BYTES // (1024*1024)}MB size limit" | |
| ) |
1 participant
🚨 Severity: CRITICAL
💡 Vulnerability: Checking file sizes using
path.stat().st_sizeprior to reading exposes a Time-Of-Check to Time-Of-Use (TOCTOU) vulnerability. This can also lead to an Out-Of-Memory Denial of Service (DoS) attack if a malicious device file like/dev/zerois used (which incorrectly reports size 0).🎯 Impact: Attackers or malformed user configurations could crash the application by filling memory entirely.
🔧 Fix: Replaced
path.stat().st_sizewithpath.is_file()to ensure it's a regular file, and implemented a strict, bounded read usingf.read(limit + 1)which effectively caps the memory read. If the length of the read content exceeds the limit, it throws a ValueError. Inline comments were added to explain the security boundaries.✅ Verification: Ran format, lint, mypy, and pytest to ensure existing tests pass and the behavior remains correct.
PR created automatically by Jules for task 5942739343146413877 started by @ivangegovdve-sudo