Zero-day vulnerability in Microsoft Exchange Server

Server-Side Request Forgery (SSRF)
CVE-2021-26855

Vulnerability details

Advisory: SB2021030301 - Multiple vulnerabilities in Microsoft Exchange Server

Vulnerable component: Microsoft Exchange Server

CVE-ID: CVE-2021-26855

CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:H/RL:O/RC:C

CWE-ID: CWE-918 - Server-Side Request Forgery (SSRF)

Description:

The vulnerability allows a remote attacker to execute arbitrary code on the system.

The vulnerability exists due to insufficient validation of user-supplied input. A remote attacker can send specially crafted HTTP request to the Microsoft Exchange OWA interface, upload arbitrary file on the server and execute it.

Note, this vulnerability is being actively exploited in the wild.

Public Exploits:

- Microsoft Exchange 2019 - Unauthenticated Email Download (Metasploit) [Exploit-DB]

- Microsoft Exchange 2019 - Unauthenticated Email Download [Exploit-DB]

External links:

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26855

About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.