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fix(path-validation): resolve symlinks in assertWithinDir #184

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fix(path-validation): resolve symlinks in assertWithinDir #184

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6 changes: 4 additions & 2 deletions src/lib/path-validation.ts
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Original file line number Diff line number Diff line change
@@ -1,13 +1,15 @@
import fs from 'fs';
import path from 'path';

/**
* Validates that a resolved path is within the given directory.
* Follows symlinks to prevent symlink-based path traversal.
* Throws if the path escapes the directory (path traversal).
* Returns the resolved (normalized) path.
*/
export function assertWithinDir(targetPath: string, allowedDir: string): string {
const resolved = path.resolve(targetPath);
const dir = path.resolve(allowedDir);
const resolved = fs.realpathSync(targetPath);
const dir = fs.realpathSync(allowedDir);
if (!resolved.startsWith(dir + path.sep) && resolved !== dir) {
throw new Error(`Path traversal detected: ${resolved} is outside allowed directory ${dir}`);
}
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