CVE-2026-42897: Microsoft Exchange Server Cross-Site Scripting Vulnerability
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
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.
Description quoted from the CVE record (assigned by microsoft, published 2026-05-14).
Weakness: CWE-79: Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’)
How it can be exploited
Exploitable over the network with low attack complexity needing no privileges and a user must take an action. Impact: confidentiality high, integrity high, availability none. 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
CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: no. Technical impact: total.
- On CISA KEV since
- 2026-05-15
- US federal deadline
- 2026-05-29
- Ransomware use
- Not known
Public exploit evidence (Exploit Observer)
Also known as: BDU:2026-06919, EUVD-2026-30343, GHSA-3c39-338m-m4vp
Exploit Observer links 1 piece of public exploit code or detection modules that name this CVE or one of its aliases.
Exploit code and modules (1)
Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.
- Code repository: https://github.com/atiilla/cve-2026-42897
Research and write-ups (2)
- Research or write-up: https://ptsecurity.com/research/trending-vulnerabilities/CVE-2026-42897
- Research or write-up: https://undercodetesting.com/zero-day-alert-cve-2026-42897-turns-exchange-servers-into-silent-cyber-weapons-no-patch-in-sight-video
Vulnerability databases and vendor advisories (5)
Catalogue entries, not exploit evidence.
- Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2026-30343
- Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-3c39-338m-m4vp
- Vulnerability database or vendor advisory: https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2026-42897
- Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-42897
- Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-42897
13 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.
VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.
Live scores
- EPSS
- 0.707
very likely to be attacked soon - VEDAS
- 0.681
some exploit evidence - On CISA KEV
- Yes, since 2026-05-15
- Detection rule
- None yet
Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish.
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| Microsoft Microsoft Exchange Server 2016 Cumulative Update 23 | from 15.01.0.0 before 15.01.2507.069 | Not stated |
| Microsoft Microsoft Exchange Server 2019 Cumulative Update 14 | from 15.02.0.0 before 15.02.1544.041 | Not stated |
| Microsoft Microsoft Exchange Server 2019 Cumulative Update 15 | from 15.02.0.0 before 15.02.1748.046 | Not stated |
| Microsoft Microsoft Exchange Server Subscription Edition RTM | from 15.02.0.0 before 15.02.2562.043 | Not stated |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
Exploit Observer also maps it to: microsoft exchange_server, microsoft exchange_server_subscription_edition, microsoft_corp microsoft_exchange_server_2016_cumulative_update_23, microsoft_corp microsoft_exchange_server_2019_cumulative_update_14, microsoft_corp microsoft_exchange_server_2019_cumulative_update_15, microsoft_corp microsoft_exchange_server_subscription_edition_rtm.
How to fix it
Fixed versions stated in the CVE record: 15.01.2507.069, 15.02.1544.041, 15.02.1748.046, 15.02.2562.043.
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.
Vendor guidance:
- Microsoft Exchange Server Spoofing Vulnerability (vendor-advisory, patch)
How to detect it
There is no open VEDAS detection rule for this bug yet. It is listed on the detection gaps page if CISA has confirmed attacks.
References
Vendor advisories and patches
- Microsoft Exchange Server Spoofing Vulnerability (vendor-advisory, patch)
Government sources
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-42897 (government-resource)
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.