Final answer:
In CVSS2 notation, 'Au:N' means attackers do not need to authenticate to exploit the vulnerability, representing a high risk within the scoring system. Authentication plays a critical role in security, with non-authentication required vulnerabilities posing greater threats.
Step-by-step explanation:
In CVSS2#AV:N/AC:L/Au:N/C:P/I:N/A:N, the notation Au:N indicates that attackers do not need to authenticate to exploit the vulnerability. This is the most serious value for this metric within the CVSS (Common Vulnerability Scoring System) framework. Authentication is a key aspect in security, and vulnerabilities that do not require an attacker to authenticate pose a higher risk, since they can be exploited by anyone with network access to the system. The implication of Au:N in a CVSS score is that the barrier to entry for an attack is low, making it more likely that the vulnerability can be exploited by unskilled attackers, thereby increasing the potential reach and impact of the attack.