Coordination is defined by Merriam-Webster as:
the process of organizing people or groups so that they work together properly and well
Vulnerability Coordination is the process by which multiple stakeholders in a software vulnerability work together to analyze and address a vulnerability with the goal of eventually disclosing to the public the existence of the vulnerability and guidance on how to mitigate or fix the vulnerability.
Vulnerabilities are difficult to define, but a vulnerability may be thought of as a flaw in software or hardware components that allows an attacker to perform actions that wouldn't normally be allowed. The impact of such vulnerabilities varies greatly, from being able to learn someone's private email address, to taking control of a computer, to causing physical damage and bodily injury.
The stakeholders vary on a case by case basis, but typically include:
The CERT/CC's role in coordination is to coordinate these stakeholders, making sure the issue is addressed accordingly and the correct information reaches the public.
Vulnerability Disclosure is the process by which information about the vulnerability (and advice for mitigating or fixing the vulnerability) are released to consumers of the product, and more generally, the general public at large.
There is no specific way to do this; sometimes, vulnerability information is disclosed in a blog post by the reporter of the vulnerability, or emailed to a security mailing list. Sometimes the vendor issues a security advisory to its customers or to the public. In the CERT/CC's case, we publish Vulnerability Notes on our website, usually in coordination with other simultaneous disclosure methods by the reporter or the vendor.
The amount of information in a disclosure also varies greatly. Some disclosures only warn of a general vulnerability in some specific software; others are more specific and provide actual examples of how to attack the flaw (the examples are called "proof of concept", usually shortened to "PoC").
There is general disagreement on what the "proper" way to disclose a vulnerability is in the security community, as different people and organizations harbor sometimes very strongly differing opinions. As the oldest software vulnerability coordinator in the world, the CERT/CC regularly discusses such issues and opinions with many stakeholders.
A number of philosophies exist regarding the disclosure of software vulnerabilities to the public. A few of them are listed below:
Another take on this issue is provided at Wikipedia.
The CERT/CC believes the Coordinated Disclosure process is the best balance of these competing interests. The public and especially users of the vulnerable component deserve to know issues with their products and how the vendor handles said issues, but at the same time, quickly disclosing such information without review and mitigation only opens the public up to exploit. The best scenario is when everyone can coordinate and work together to protect the public. This coordination can also often be turned into a public relations win for the vendor by quickly addressing the issue.