Threat Intelligence / CVE / CVE-2021-42278

CVE-2021-42278 — Microsoft Windows Server 2004

CISA KEVRansomware
CVSS v3.1 7.5 (HIGH) · EPSS 94.0% (higher than 99.9% of all scored CVEs) · Priority 10/10 · Published 2021-11-10

As of 2025-10-30, CVE-2021-42278 is a HIGH-severity vulnerability in Microsoft Windows Server 2004, CVSS v3.1 7.5, EPSS 94.0% (99.9th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-04-11), with a US federal remediation deadline of 2022-05-02, and CISA links it to known ransomware campaigns. Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2021-42278, most recently “PaperCut NG/MF Chained Zero-Day RCE (CVE-2026-82078 & CVE-2026-81578) Under Active Exploitation”.

Last updated: 2025-10-30

What is CVE-2021-42278?

Active Directory Domain Services Elevation of Privilege Vulnerability

The record classifies CVE-2021-42278 under weakness class NVD-CWE-noinfo. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 9 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 1767 days ago.

Severity and exploitation probability

CVSS v3.1 base score
7.5 — HIGH
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (FIRST)
94.0% probability of exploitation in the next 30 days, higher than 99.9% of all scored CVEs
CISA KEV
Listed since 2022-04-11, federal remediation deadline 2022-05-02 — used in known ransomware campaigns
Threadlinqs priority
10/10 — CISA lists it as used in ransomware, which Threadlinqs scores at the maximum
Published
2021-11-10, last modified 2025-10-30

Is CVE-2021-42278 being exploited?

CISA added CVE-2021-42278 to the Known Exploited Vulnerabilities catalog on 2022-04-11, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2022-05-02 under BOD 22-01. CISA flags the vulnerability as one used in known ransomware campaigns. It currently carries a trending score of 40 in the Threadlinqs vulnerability feed.

Affected products and versions

How to fix CVE-2021-42278

The record marks a vendor fix as available for CVE-2021-42278. Patch reference: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42278. Vendor advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-42278. Because CVE-2021-42278 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2022-05-02. 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-2021-42278

2 tracked threats in the Threadlinqs corpus reference CVE-2021-42278, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Seeded from nvd and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2021-42278 are available via the Threadlinqs MCP server (Purple tier). View plans →

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