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Executive Summary
CVE-2021-31207 is a security feature bypass vulnerability in Microsoft Exchange Server that has been actively exploited in the wild. This vulnerability is part of the ProxyShell exploit chain, which also includes CVE-2021-34473 and CVE-2021-34523. The vulnerability allows an attacker to bypass security features and potentially execute arbitrary code on the affected system. The ProxyShell exploit chain has been leveraged in various ransomware campaigns and other malicious activities, making it crucial for organizations to understand and mitigate this threat.
Technical Information
CVE-2021-31207 is a security feature bypass vulnerability in Microsoft Exchange Server. The vulnerability is identified by the CVE ID: CVE-2021-31207 and has a CVSS v3.1 Base Score of 6.6, indicating a medium severity level. The vulnerability is classified under CWE-434 - Unrestricted Upload of File with Dangerous Type. The affected software versions include Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2016 Cumulative Update 19 and 20, and Microsoft Exchange Server 2019 Cumulative Update 8 and 9.
The vulnerability allows an attacker to bypass security features and potentially execute arbitrary code on the affected system. This is achieved by exploiting the ProxyShell exploit chain, which involves three vulnerabilities: CVE-2021-34473, CVE-2021-34523, and CVE-2021-31207. Once the initial vulnerabilities (CVE-2021-34473 and CVE-2021-34523) are exploited, CVE-2021-31207 allows the attacker to write files and execute arbitrary code on the server.
The attack vector for this vulnerability is network-based (AV:N), with a high attack complexity (AC:H) and requiring high privileges (PR:H). There is no user interaction required (UI:N), and the scope is unchanged (S:U). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H).
Exploitation in the Wild
CVE-2021-31207 has been actively exploited in the wild as part of the ProxyShell attack chain. Attackers use this vulnerability in conjunction with CVE-2021-34473 and CVE-2021-34523 to gain initial access to the Exchange server and then execute arbitrary code.
Notable exploits and attacks include the ProxyShell Exploit Chain, where attackers exploit three vulnerabilities in Microsoft Exchange Server. Once the initial vulnerabilities (CVE-2021-34473 and CVE-2021-34523) are exploited, CVE-2021-31207 allows the attacker to write files and execute arbitrary code on the server. This exploit chain has been detailed in various sources, including the ProxyShell Exploit Details.
Additionally, CVE-2021-31207 has been leveraged in ransomware campaigns, where attackers gain access to the Exchange server and deploy ransomware to encrypt data and demand ransom. More details can be found in the CVE Details.
APT Groups using this vulnerability
Various APT groups have been known to exploit vulnerabilities in Microsoft Exchange Server, including those involved in ransomware campaigns. These groups target sectors such as government, healthcare, finance, and critical infrastructure across multiple countries. The exploitation of CVE-2021-31207 by these groups underscores the importance of timely patching and robust security measures.
Affected Product Versions
The affected product versions for CVE-2021-31207 include: - Microsoft Exchange Server 2013 Cumulative Update 23 - Microsoft Exchange Server 2016 Cumulative Update 19 and 20 - Microsoft Exchange Server 2019 Cumulative Update 8 and 9
Workaround and Mitigation
To mitigate the risk associated with CVE-2021-31207, it is crucial to apply the patches released by Microsoft. The patches address this vulnerability and are available in the Microsoft Security Response Center.
In addition to applying patches, organizations should regularly monitor their Exchange servers for any signs of compromise, such as unusual file uploads or changes in configuration. Network segmentation can also help isolate Exchange servers from the rest of the network, limiting the potential impact of an exploit.
References
For further reading and detailed information, please refer to the following sources: - National Vulnerability Database (NVD): NVD CVE-2021-31207 - Microsoft Security Response Center: MSRC CVE-2021-31207 - Zero Day Initiative: ZDI-21-819 - Packet Storm Security: ProxyShell Remote Code Execution - Google Cloud Blog: ProxyShell Exploit Details - FortiGuard Labs: ProxyShell Threat Signal Report
Rescana is here for you
At Rescana, we understand the critical importance of protecting your organization from cybersecurity threats. Our Continuous Threat and Exposure Management (CTEM) platform helps you stay ahead of potential vulnerabilities and ensures that your systems are secure. If you have any questions about this report or any other issue, please do not hesitate to contact us at ops@rescana.com. We are here to assist you in safeguarding your digital assets.
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