The first step when a new vulnerability is identified is to re-evaluate the risk associated with the vulnerability. This may require an update to the risk assessment and the implementation of additional controls. Informing senior management of the vulnerability is important, but should not be the first step. Implementing compensating controls may also be necessary, but again, should not be the first step. Asking the business owner for a remediation plan may be useful, but only after the risk has been re-evaluated.
The information security manager should first re-evaluate the risk posed by the new vulnerability to determine its impact and likelihood. Based on this assessment, appropriate actions can be taken such as informing senior management, implementing compensating controls, or requesting a remediation plan from the business owner. The other choices are possible actions but not necessarily the first one.
A vulnerability is a weakness that can be exploited by an attacker to compromise a system or network2. A vulnerability can affect key data processing systems within an organization if it exposes sensitive information, disrupts business operations, or damages assets2. A vulnerability assessment is a process of identifying and evaluating vulnerabilities and their potential consequences2

The greatest concern for an information security manager in this situation would be the security of the data that is being processed by the third-party service provider working from a remote site. This could be a concern because the data may not be adequately protected from unauthorized access, manipulation, or theft. A secure communications protocol should be used to ensure the confidentiality and integrity of the data in transit. Additionally, the information security manager should ensure that the third-party service provider has appropriate security controls in place to protect the data, such as access controls, error checking, and malware protection. This information can be found in the ISACA's Certified Information Security Manager (CISM) Study Manual, Section 5.2.

The primary advantage of single sign-on (SSO) is that it increases the efficiency of access management. With SSO, users only need to remember one set of credentials to access all of their applications, rather than having to remember multiple usernames and passwords for each application. This simplifies the user experience and helps to reduce the amount of time spent managing access to multiple applications. Additionally, SSO can also increase the security of related applications, as users are not sharing the same credentials across multiple applications, and it can also support multiple authentication mechanisms, such as biometric authentication.