What is CVE-2026-42897?
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.
The record classifies CVE-2026-42897 under weakness class CWE-79. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first, and has high impact on confidentiality, integrity. 4 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 177 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 8.1 — HIGH
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 - EPSS (FIRST)
- 5.6% probability of exploitation in the next 30 days, higher than 91.9% of all scored CVEs
- CISA KEV
- Listed since 2026-05-15, federal remediation deadline 2026-05-29
- Threadlinqs priority
- 9/10 — CISA KEV-listed, which Threadlinqs floors at 9
- Published
- 2026-05-14, last modified 2026-06-19
Is CVE-2026-42897 being exploited?
CISA added CVE-2026-42897 to the Known Exploited Vulnerabilities catalog on 2026-05-15, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2026-05-29 under BOD 22-01. Weaponised exploit code for CVE-2026-42897 is publicly available. 1 public proof-of-concept repository is tracked for this identifier. It currently carries a trending score of 64 in the Threadlinqs vulnerability feed.
- atiilla/CVE-2026-42897 (github)
Affected products and versions
- Microsoft: Exchange Server 2016 Cumulative Update 23, Exchange Server 2019 Cumulative Update 14, Exchange Server 2019 Cumulative Update 15, Exchange Server Subscription Edition RTM
How to fix CVE-2026-42897
Patch reference: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42897. Because CVE-2026-42897 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2026-05-29. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-42897
4 tracked threats in the Threadlinqs corpus reference CVE-2026-42897, either in the campaign’s CVE list or as an indicator on the campaign record.
- NSFOCUS Monthly APT Insights August 2026: Lazarus MISTPEN/ForestTiger/RelayShell Campaign with CVE-2026-68820, UAC-0099 LUNCHPOKE/BURNYBEAR/MATCHBOIL.V2, CVE-2026-42897 Exchange OWA Exploitation — HIGH · 2026-10-21
- Pro-Ukraine 'Hacking Cat' Group Deploys Gorilla RAT, Monkey Ransomware, and Nemo Wiper Against Russian Targets via Exchange/SharePoint Exploitation — HIGH · 2026-09-15
- Russian TA488 (Void Blizzard / Laundry Bear) Exploits Exchange OWA Zero-Day (CVE-2026-42897) with OWAReaper Backdoor for Long-Term Mailbox Access — CRITICAL · 2026-07-29
- Microsoft Exchange Server OWA Cross-Site Scripting Zero-Day CVE-2026-42897 Exploited In the Wild — CRITICAL · 2026-06-11
Sources
Enriched from CVE.org, NVD, FIRST EPSS, CISA KEV, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.