This vulnerability affects the mg_aes_gcm_decrypt function in the /src/tls_aes128.c file of Cesanta Mongoose versions up to 7.20. It causes improper verification of the GCM authentication tag, which is critical for ensuring the integrity and authenticity of encrypted data. An attacker could potentially exploit this flaw remotely, although the attack complexity is high and no privileges or user interaction are required. The vendor has confirmed the issue and fixed it in version 7.21.

Improper verification of the cryptographic signature may allow an attacker to bypass authentication checks on encrypted data, potentially leading to data integrity violations. However, the CVSS score of 6.3 and the medium severity rating indicate that exploitation is difficult and the impact is limited to integrity with no direct confidentiality or availability impact stated.

Upgrade Cesanta Mongoose to version 7.21 or later, as this version contains the official fix for the vulnerability. Since the vendor has confirmed the fix, applying this update is the recommended remediation. No additional mitigations are specified or required.