fix: prevent symlink escape in Filesystem.contains #6403
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The `Filesystem.contains()` function previously performed only lexical path checking, which could be bypassed using symlinks inside the project directory. An attacker could create a symlink pointing to sensitive files outside the project (e.g., ~/.ssh/id_rsa), and the file tools would allow reading them. This fix: - Uses `realpathSync` to resolve symlinks before checking containment - Falls back to lexical check if realpath fails (e.g., file doesn't exist) - Adds explicit handling for Windows cross-drive paths (D:\ vs C:\) - Removes the TODO comments that documented this issue
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Pull request overview
This PR addresses a critical security vulnerability where the Filesystem.contains() function could be bypassed using symlinks within the project directory, potentially allowing access to sensitive files outside the project boundaries.
Key Changes:
- Implements symlink resolution using
realpathSyncbefore path containment checks - Adds Windows-specific handling for cross-drive path detection
- Removes TODO comments that documented the vulnerability
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| packages/opencode/src/util/filesystem.ts | Enhanced contains() function with symlink resolution via realpathSync and Windows cross-drive path detection |
| packages/opencode/src/file/index.ts | Removed TODO comments about the symlink escape vulnerability that has now been addressed |
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- Extract duplicated Windows cross-drive and relative path check into isContained() helper function - Resolve parent and child paths independently for better security (use resolved parent even when child doesn't exist yet) - Simplifies the code and addresses Copilot review feedback Signed-off-by: Jay Hemnani <jayhemnani9910@gmail.com>
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The
Filesystem.contains()function previously performed only lexical path checking, which could be bypassed using symlinks inside the project directory. An attacker could create a symlink pointing to sensitive files outside the project (e.g., ~/.ssh/id_rsa), and the file tools would allow reading them.This fix:
realpathSyncto resolve symlinks before checking containment