Security Vulnerability: Path Traversal Risk in Character Service Image Upload

A critical security flaw in the character service's image upload function exposes servers to potential compromise. The vulnerability, identified in `character_service.py`, stems from inadequate validation that could allow attackers to bypass directory restrictions and upload files to arbitrary locations on the server. This path traversal weakness creates a direct vector for unauthorized file access and, in the worst case, remote code execution if malicious files reach web-accessible directories.

The vulnerability is rooted in multiple validation failures. First, the file extension check is case-sensitive, allowing attackers to potentially bypass filters using uppercase extensions like `.PNG` or `.JPG`. More critically, the filename sanitization logic fails to prevent directory traversal attempts using sequences like `../`. Combined with a lack of validation to ensure the final file path remains within the designated upload directory, this creates a clear path for exploitation.

If exploited, this flaw could lead to server compromise, data theft, or service disruption. The immediate risk is elevated for any deployment using the affected `character_service.py` module without additional external safeguards. While the source does not confirm active exploitation, the described vulnerability pattern is a well-known attack vector that demands urgent remediation to prevent potential security incidents.