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

Q: How do I fix CVE-2026-42897?

exchange server: downgrade or apply the listed mitigation; exchange server subscription edition: upgrade to 15.02.2562.043. Exact commands for each OS are on this page.

Q: Is CVE-2026-42897 being exploited?

Yes. CVE-2026-42897 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2026-42897 affect?

CVE-2026-42897 affects exchange server, exchange server subscription edition. Severity is high (CVSS 8.1). 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.

Q: How urgent is CVE-2026-42897?

Priority 83/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); On your watchlist

Patch now

HIGH 8.1EXPLOITEDWATCHLISTDOWNGRADEUPGRADE

CVE-2026-42897 is a high-severity flaw (CVSS 8.1) affecting exchange server, exchange server subscription edition, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	70.7% (top 1%)
CISA exploited list	Yes, fix due 2026-05-29
Weakness	CWE-79
Published	2026-05-14
Last modified	2026-10-26

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-14 18:16 UTCPublished CVE record published
2026-05-15Exploited Added to the CISA Known Exploited Vulnerabilities list
2026-05-29Deadline CISA due date for US federal agencies to patch
2026-10-26 14:10 UTCUpdated Record last modified

microsoft exchange server DOWNGRADE

Affected: 2016 · 2016 cumulative_update_1 · 2016 cumulative_update_10 · 2016 cumulative_update_11 · 2016 cumulative_update_12 · 2016 cumulative_update_13 · 2016 cumulative_update_14 · 2016 cumulative_update_15

Fixed in: no fixed release known

Safe to downgrade to: a release before 2016

1. Check installed version

apt-cache policy exchange-server || rpm -q exchange-server || exchange-server --version

2. No fixed release: DOWNGRADE to a release before 2016 (Debian / Ubuntu)

apt-cache madison exchange-server sudo apt install exchange-server=<VERSION_BEFORE_2016> sudo apt-mark hold exchange-server

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list exchange-server sudo dnf downgrade exchange-server-<VERSION_BEFORE_2016> sudo dnf versionlock add exchange-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

microsoft exchange server subscription edition UPGRADE

Affected: < 15.02.2562.043

Fixed in: 15.02.2562.043

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy exchange-server-subscription-edition || rpm -q exchange-server-subscription-edition || exchange-server-subscription-edition --version

2. UPGRADE to 15.02.2562.043 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade exchange-server-subscription-edition

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade exchange-server-subscription-edition

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Microsoft Exchange Server 2016 Cumulative Update 23 · KB5094144 · FIXED · 15.01.2507.069 · KB5094144

Install KB5094144 via Windows Update, then verify: Get-HotFix -Id KB5094144

Microsoft Exchange Server 2019 Cumulative Update 14 · KB5094142 · FIXED · 15.02.1544.041 · KB5094142

Install KB5094142 via Windows Update, then verify: Get-HotFix -Id KB5094142

Microsoft Exchange Server 2019 Cumulative Update 15 · KB5094140 · FIXED · 15.02.1748.046 · KB5094140

Install KB5094140 via Windows Update, then verify: Get-HotFix -Id KB5094140

Microsoft Exchange Server Subscription Edition RTM · KB5094139 · FIXED · 15.02.2562.043 · KB5094139 · source

Install KB5094139 via Windows Update, then verify: Get-HotFix -Id KB5094139

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: atiilla/CVE-2026-42897 (5 stars)

Advisories and coverage

Official advisories

CERT-FR Alerts: [Màj] Vulnérabilité dans Microsoft Exchange Server (15 mai 2026) 2026-05-15
CERT-FR Alerts: [Màj] Vulnérabilité dans Microsoft Exchange Server (15 mai 2026) 2026-05-15

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-42897?

exchange server: downgrade or apply the listed mitigation; exchange server subscription edition: upgrade to 15.02.2562.043. Exact commands for each OS are on this page.

Is CVE-2026-42897 being exploited?

Yes. CVE-2026-42897 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2026-42897 affect?

CVE-2026-42897 affects exchange server, exchange server subscription edition. Severity is high (CVSS 8.1). 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.

How urgent is CVE-2026-42897?

Priority 83/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); On your watchlist

Software pages

Microsoft Exchange vulnerabilities

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References

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