CVE-2026-42897
HIGH · 8.1 KEV EPSS 2.5%Confirmed active abuse + urgent vendor patching; KEV delay and absence of public PoC prevent higher score.
What: Cross-site scripting (XSS) in Microsoft Exchange Server on-premises allowing email spoofing; CVSS 8.1 HIGH.
Why it matters: Microsoft confirmed active exploitation in-the-wild as of 2026-05-14. Posts cite emergency patching and mitigation guidance. Not yet KEV-listed but vendor advisory + confirmed active abuse signals immediate triage priority for on-prem Exchange operators.
Where it's seen: Coordinated social chatter across security news outlets (HelpNetSecurity, The Hacker News) and Bluesky; consistent framing of "actively exploited zero-day" with remediation paths (EOMT, service updates). No public PoC mentioned, but threat actor activity confirmed by Microsoft.
RISK: HIGH — Active exploitation of high-CVSS spoofing flaw in widely-deployed messaging infrastructure.
Description
Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
CVSS 3.1 breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N- Attack vector
- Network
- Complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- None