CVE-2025-27837

What it actually does

The flaw permits access to arbitrary files on the system by supplying a truncated file path containing invalid UTF-8 characters, bypassing normal path validation in the affected code paths.

Why it matters to the business

Attackers may read sensitive configuration or data files, increasing the risk of information disclosure and subsequent attacks on affected systems.

How an attack unfolds

An attacker supplies a specially crafted path string that is truncated and contains invalid UTF-8 sequences to the vulnerable path-handling routines, resulting in unauthorized file access without triggering normal security checks.

How to fix it

Upgrade vyper (PyPI) to the fixed commit 3d9c537142fb99b2672f21e2057f5f202cde194f. Verify the installed version matches a patched release and test the application after upgrade.

How to confirm the fix worked

Confirm the installed version is at or above the fixed commit, review path-handling code for UTF-8 truncation checks, and perform functional tests with malformed path inputs to ensure access is denied.

Typical attack path

1. Identify an entry point that accepts file paths or names
2. Construct a truncated path containing invalid UTF-8 characters
3. Submit the crafted input to the vulnerable component
4. Read or access files outside the intended directory

How to detect it

Review application and system logs for file-open attempts that contain truncated paths or invalid UTF-8 sequences; look for unexpected access to files outside normal application directories.

What your security team should do

• Apply the listed fixed version immediately given the public disclosure date
• Scan all instances of the affected package for the vulnerable version
• Add monitoring for unexpected file access attempts in application logs