Anatomy of an Automated Patch: Fixing a File Upload RCE CVE-2025-59304

The best security alerts are the ones that come with a fix. Our platform recently discovered and automatically generated a patch for a critical RCE in Swetrix Web Analytics. This post dissects the vulnerability (a classic Path Traversal), the exploit, and the code for the automated patch.

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The Vulnerable Code

The root cause was a single line in the CdnService.uploadFile method. The code used an unsanitized, user-controlled filename to construct a file path on the server.

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backend/apps/cloud/src/marketplace/cdn/cdn.service.ts

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This is a textbook Path Traversal vulnerability (CWE-22).

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The Exploit

Since file.originalName wasn't sanitized, an attacker could use path traversal sequences (../) to write a file anywhere on the filesystem.

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This leads directly to RCE in four steps:

1. Craft a payload, like a JavaScript reverse shell
2. Identify an executable file on the server, like the application's entry point (e.g., entrypoint.js)
3. Upload the payload from step 1 with a malicious filename, overwriting the file from step 2 (e.g., ../../app/entrypoint.js)
4. Achieve remove code execution when the application restarts and loads the overwritten file

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The Fix: Don’t Trust User Input

The fix is to never use user-provided input in file paths. Our platform automatically generated the following secure code:

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backend/apps/cloud/src/marketplace/cdn/cdn.service.ts

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This approach eliminates the vulnerability entirely. You can see the full patch in Pull Request #397 on GitHub.

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Foundational bugs like this remain critical, but finding them is only half the battle. We're building tools to automate the entire process, from discovery to fix.