CVE-2021-40818: 
Linux Debian vulnerability analysis and mitigation

CVE-2021-40818 affects the Glewlwyd SSO server through version 2.5.3. The vulnerability is a buffer overflow that occurs during FIDO2 signature validation in the webauthn registration process, specifically in the scheme/webauthn.c component (NVD). The issue was discovered and disclosed on September 8, 2021.

The vulnerability exists in the checkattestationfidou2f function within scheme/webauthn.c where a fixed-size buffer datasigned[200] was used without proper size validation. The issue was fixed by replacing the fixed buffer with dynamically allocated memory sized according to the actual data requirements (rpidhashlen + clientdatahashlen + credentialidlen + certxlen + certy_len + 2) (GitHub Commit).

A successful exploitation of this buffer overflow vulnerability could potentially lead to memory corruption during the FIDO2 signature validation process in webauthn registration. This could affect the security of the authentication system (Debian Bug).

The vulnerability was fixed in subsequent releases after version 2.5.3. Users should upgrade to a patched version. For Debian systems, the fix was included in glewlwyd version 2.5.2-3 (Debian Bug).