Proxyshell Vulnerabilities- Summary

Non-Technical Advice

The vulnerabilities described on this and the following page are known as the Proxyshell vulnerabilities of the on-premises Microsoft Exchange email server. If you have a Microsoft Exchange email server on-site (rather than in the ‘cloud’ through Microsoft 365) you may be at risk of these vulnerabilities being exploited.

While this is a collection of three vulnerabilities, the highest risk vulnerability has been independently scored as posing a critical risk to most organisations.

The Operation Configured team have contacted you because research indicates that your organisation may have these vulnerabilities and the server is exposed to the public internet. While it is possible that this information is incorrect because of the method of vulnerability identification employed by the Operation, it is important you establish for yourself whether your organisation is vulnerable. If you establish that your systems are vulnerable, there is an increased risk you will fall victim to a potentially devastating criminal cyber attack.

There is another technically focused summary of these vulnerabilities available for ICT and other technical teams. You should use them to support you in making choices about how to approach this situation.

IMPORTANT: While SEROCU are notifying organisations of this vulnerability, the team will NOT be asking for any information or other details. They will only be providing information. Any unsolicited contact claiming to be from the Police should always be treated with caution. For more information read about Verifying Authenticity.

About these Vulnerabilities

In 2021 researchers detected the exploitation of a further three technical vulnerabilities being used to attack on-premises versions of the Microsoft Exchange Server in targeted attacks (in addition to the Proxylogon vulnerabilities discovered earlier in the year). Microsoft Exchange is predominantly an email server, but does provide some other functionality.

In the attacks observed, the criminals, often referred to as ‘threat actors’, used these vulnerabilities to access on-premises Exchange servers which enabled access to email accounts. The criminals could also further exploit the server in a way which allowed them to install additional malicious software (‘malware’) to facilitate long-term access to the wider network and systems of their victims.

The Risk these Vulnerabilities pose

There are significant risks should you choose to ignore or accept these vulnerabilities remaining in your system. Criminals are known to be actively scanning for vulnerable Exchange email servers and using them to attack organisations. Consequences may include, but are not limited to:

  • Theft of your data
  • Corruption of your backups
  • Using you to attack others you work with, damaging your reputation
  • Ransomware attack against your systems
  • Fines from regulators such as the Information Commissioner’s Office (ICO)
  • Your organisation ceasing operations because of system failure, reputational damage or financial losses

News Reporting of Exploitation of these Vulnerabilities


Next Steps

The next steps for your organisation should be to:

  1. Verify the presence of these vulnerabilities in your organisation; if so:
  2. Establish if these vulnerabilities has already been exploited on your systems
  3. Work with your ICT team or provider to establish the degree of threat, potential harm and risk posed to your organisation
  4. Isolate and mitigate the risk as soon as possible
  5. Establish a plan to resolve these vulnerabilities and eliminate the risk
  6. Plan to improve your cybersecurity for the future

For more information: