Hackers Actively Searching for Unpatched Microsoft Exchange Servers

Threat actors are actively carrying out opportunistic scanning and exploitation of Exchange servers employing a new exploit chain leveraging a trio of flaws impacting on-premises installations, generating them the most recent set of bugs after ProxyLogon vulnerabilities were being exploited en masse at the begin of the yr.

The distant code execution flaws have been collectively dubbed “ProxyShell.” At minimum 30,000 machines are affected by the vulnerabilities, in accordance to a Shodan scan performed by Jan Kopriva of SANS Web Storm Middle.

“Begun to see in the wild exploit tries from our honeypot infrastructure for the Exchange ProxyShell vulnerabilities,” NCC Group’s Richard Warren tweeted, noting that one of the intrusions resulted in the deployment of a “C# aspx webshell in the /aspnet_consumer/ listing.”

Patched in early March 2021, ProxyLogon is the moniker for CVE-2021-26855, a server-aspect ask for forgery vulnerability in Trade Server that permits an attacker to get management of a susceptible server as an administrator, and which can be chained with a different post-authentication arbitrary-file-write vulnerability, CVE-2021-27065, to attain code execution.

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The vulnerabilities arrived to mild right after Microsoft spilled the beans on a Beijing-sponsored hacking operation that leveraged the weaknesses to strike entities in the U.S. for needs of exfiltrating facts in what the company explained as minimal and targeted assaults.

Considering the fact that then, the Windows maker has preset 6 more flaws in its mail server element, two of which are called ProxyOracle, which enables an adversary to get better the user’s password in plaintext structure.

A few other difficulties — acknowledged as ProxyShell — could be abused to bypass ACL controls, elevate privileges on Exchange PowerShell backend, successfully authenticating the attacker and permitting for distant code execution. Microsoft mentioned that each CVE-2021-34473 and CVE-2021-34523 were inadvertently omitted from publication right until July.

ProxyLogon:

  • CVE-2021-26855 – Microsoft Trade Server Distant Code Execution Vulnerability (Patched on March 2)
  • CVE-2021-26857 – Microsoft Exchange Server Remote Code Execution Vulnerability (Patched on March 2)
  • CVE-2021-26858 – Microsoft Exchange Server Remote Code Execution Vulnerability (Patched on March 2)
  • CVE-2021-27065 – Microsoft Exchange Server Remote Code Execution Vulnerability (Patched on March 2)

ProxyOracle:

  • CVE-2021-31195 – Microsoft Trade Server Distant Code Execution Vulnerability (Patched on May 11)
  • CVE-2021-31196 – Microsoft Trade Server Remote Code Execution Vulnerability (Patched on July 13)

ProxyShell:

  • CVE-2021-31207 – Microsoft Trade Server Stability Aspect Bypass Vulnerability (Patched on May perhaps 11)
  • CVE-2021-34473 – Microsoft Exchange Server Distant Code Execution Vulnerability (Patched on April 13, advisory produced on July 13)
  • CVE-2021-34523 – Microsoft Trade Server Elevation of Privilege Vulnerability (Patched on April 13, advisory introduced on July 13)

Other:

  • CVE-2021-33768 – Microsoft Trade Server Elevation of Privilege Vulnerability (Patched on July 13)

At first shown at the Pwn2Individual hacking levels of competition this April, technical aspects of the ProxyShell assault chain were disclosed by DEVCORE researcher Orange Tsai at the Black Hat United states 2021 and DEF CON safety conferences previous 7 days. To protect against exploitation attempts, businesses are really advisable to install updates produced by Microsoft.

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