---
title: "CVE-2026-42897: Microsoft Exchange Server Cross-Site Scripting Vulnerability"
url: https://erroneo.us/security/cve/CVE-2026-42897/
description: "CVE-2026-42897 (Microsoft Microsoft): Exploited in the wild (CISA KEV). Improper neutralization of input during web page generation ('cross-site scripting')…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-05-14
date_modified: 2026-08-10
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-42897"
kev: true
cvss: 8.1
epss: 0.00519
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-42897: Microsoft Exchange Server Cross-Site Scripting Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Microsoft Microsoft. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2026-05-15, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2026-05-29 ; treat that as the outer limit, not the target.
- EPSS 0.5% , percentile 43: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 43% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Needs a user to click or open something. Phishing makes that realistic, but it is not wormable.

## What it is

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.

## Affected products (CVE record)

- Microsoft Microsoft Exchange Server 2016 Cumulative Update 23: 15.01.0.0 < 15.01.2507.069
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 14: 15.02.0.0 < 15.02.1544.041
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 15: 15.02.0.0 < 15.02.1748.046
- Microsoft Microsoft Exchange Server Subscription Edition RTM: 15.02.0.0 < 15.02.2562.043

## Severity

- microsoft CVSS 3.1: 8.1 `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N/E:F/RL:O/RC:C`

## Exploitation

- CISA KEV: added 2026-05-15; federal due date 2026-05-29. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.52% probability of exploitation activity in the next 30 days; percentile 43.

## Sources

- [Microsoft Exchange Server Spoofing Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42897)
- [Listed in CISA KEV notes (msrc.microsoft.com)](https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-42897)
- [Listed in CISA KEV notes (learn.microsoft.com)](https://learn.microsoft.com/en-us/exchange/plan-and-deploy/post-installation-tasks/security-best-practices/exchange-emergency-mitigation-service)
- [CVE.org record CVE-2026-42897](https://www.cve.org/CVERecord?id=CVE-2026-42897)
- [NVD entry CVE-2026-42897](https://nvd.nist.gov/vuln/detail/CVE-2026-42897)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-42897)

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Source page: https://erroneo.us/security/cve/CVE-2026-42897/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt