Actively exploitedCVSS 8.1 · HIGH

CVE-2026-42897

Microsoft Exchange Server contains a cross-site scripting vulnerability during web page generation in Outlook Web Access and when certain interaction conditions are met, arbitrary JavaScript can be executed in the browser context.

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Analysis

Microsoft Exchange Server is vulnerable to unauthenticated cross-site scripting which could lead to session hijacking or spoofing. While significant for organizations running self-hosted Exchange, it is a routine enterprise security update rather than a developer-centric emergency.

Severity

Score: 8.1(HIGH)

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

AV: NETWORK

AC: LOW

PR: NONE

UI: REQUIRED

S: UNCHANGED

C: HIGH

I: HIGH

A: NONE

Weakness (CWE): CWE-79

CISA KEV

Added to KEV: 2026-05-15

Federal patch deadline: 2026-05-29

Known ransomware use: Unknown

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.

EPSS

Probability of exploitation (next 30 days): 0.0022 (0.2%)

Percentile: 44.5%

EPSS: 2026-05-15

Affects

microsoft:exchange_server

Technical 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.

Published: 5/14/2026, 6:16:49 PM

Last modified: 5/15/2026, 7:35:52 PM

References

How to read this card

Actively exploited

KEV (Known Exploited Vulnerabilities) is CISA's catalog of CVEs confirmed as actively exploited in the real world. If a CVE is on KEV, someone is already using it in attacks.

CVSS 10.0

CVSS 10.0 — máxima severidad teórica. Explotable de forma remota, sin privilegios, con impacto total. Aún no confirmada como explotada en el mundo real, pero parchea ya.

AI-recommended

Un modelo de lenguaje revisó el CVE y consideró que afecta a software ampliamente desplegado o herramientas comunes de desarrollo. Un humano del equipo aprobó la publicación antes de que llegara aquí.

Categorías de impacto que evalúa la IA

widely_deployed_infra — kernel Linux, OpenSSL, glibc, k8s, Docker, nginx, OpenSSH.

popular_dev_tooling — Node.js, Python, Go, React, Next.js, librerías comunes de npm/pip.

common_consumer_software — Chrome, Firefox, Windows, macOS, apps móviles populares.

enterprise_saas — GitHub, GitLab, Atlassian, Salesforce, Cisco, Fortinet, Ivanti.

niche_software — CMS regionales, herramientas de hobby, librerías de poco uso.

not_relevant — firmware específico de proveedor, software descontinuado.

EPSS — EPSS (Exploit Prediction Scoring System) by FIRST.org estimates the probability that a CVE will be exploited in the next 30 days. Range is 0 to 1; very fresh CVEs typically score low until evidence accumulates.