Security advisories | Feb 27, 2020

Memory Corruption Vulnerability in Microsoft Exchange Servers

THE THREAT

On February 11th, 2020 Microsoft disclosed a Memory Corruption Vulnerability in Microsoft Exchange Servers [1]. An authenticated user could exploit this vulnerability to cause remote code execution (RCE) on vulnerable Microsoft Exchange Servers. It is probable that public exploitation of the vulnerability will occur in the near future, as proof of concept code was released on February 24th, and mass scanning was identified on February 25th.

Successful exploitation of this RCE vulnerability could lead to further compromise of the targeted systems. It is highly recommended that organizations apply the official Microsoft security patches as soon as possible to avoid being impacted.

What we’re doing about it

  • MVS (formerly esRECON) has a local plugin to detect this vulnerability
  • eSentire is currently evaluating detection methods for the exploitation of CVE-2020-0688

What you should do about it

  • After performing a business impact review, apply the official Microsoft security patches to vulnerable systems [1]

Additional information

During installation, Microsoft Exchange Server fails to generate a unique validation key. Knowledge of the default key would allow an attacker to pass arbitrary objects to be deserialized by the web application which could lead to arbitrary code execution as SYSTEM.

February 24th,2020 Proof of Concept (PoC) code was published, demonstrating exploitation of the vulnerability [2]. The next day, Twitter user @bad_packets observed mass scanning for CVE-2020-0688 [3].

For additional technical details, see the ZDI technical write up [2].

Updates for Affected Products:

  • Microsoft Exchange Server 2010 Service Pack 3 Update Rollup 30
  • Microsoft Exchange Server 2013 Cumulative Update 23
  • Microsoft Exchange Server 2016 Cumulative Update 14
  • Microsoft Exchange Server 2016 Cumulative Update 15
  • Microsoft Exchange Server 2019 Cumulative Update 3 
  • Microsoft Exchange Server 2019 Cumulative Update 4

References:

[1] https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0688

[2] https://www.thezdi.com/blog/2020/2/24/cve-2020-0688-remote-code-execution-on-microsoft-exchange-server-through-fixed-cryptographic-keys

[3] https://twitter.com/bad_packets/status/1232428319733272579