Zero-day vulnerability in Microsoft Exchange Server

Stored cross-site scripting
CVE-2026-42897

Vulnerability details

Advisory: SB2026051542 - Spoofing attack via stored XSS in Microsoft Exchange Server OWA

Vulnerable component: Microsoft Exchange Server

CVE-ID: CVE-2026-42897

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

CWE-ID: CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Description:

The disclosed vulnerability allows a remote attacker to perform cross-site scripting (XSS) attacks.

The vulnerability exists due to insufficient sanitization of user-supplied data in Outlook Web Access. A remote attacker can send a specially crafted email message and execute arbitrary JavaScript code in the victim's browser once the email is viewed. 

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

External links:

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42897

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.