Google stepped up its scrutiny of device security several years ago in the wake of the massive Stagefright vulnerability. Ever since then, Android devices list a “patch level” that tells you when its security was last updated. However, Karsten Nohl and Jakob Lell of Security Research Labs say that many devices are fibbing about their security patches. Some phones are missing more than a dozen patches.
Source: Some Android Phones Are Missing Security Patches They Claim to Have – ExtremeTech