NetEase Cloud Music client for Windows (cloudmusic.exe) versions 3.1.38 and 3.1.39.205426 contains a weak encryption vulnerability where /eapi/ and /xeapi/ API response bodies are decrypted using a fixed, publicly documented AES-128-ECB key with no integrity credential. Attackers who can intercept or originate server responses can construct valid ciphertext under the known key with PKCS#7 padding, enabling the client to accept forged API responses that serve as a prerequisite for further exploitation such as reaching the os.navigateExternal bridge.