CVE-2021-26858

As of 2025-12-18, CVE-2021-26858 is a CVSS 7.8 (HIGH-severity) vulnerability. CISA KEV-listed (known exploited). EPSS exploitation probability 53.0%. Threadlinqs Intelligence tracks 2 threats exploiting it.

Last updated: 2025-12-18

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3 vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Weaknesses (CWE)

NVD-CWE-noinfo

Exploitation status

CISA KEV-listed (known exploited)

Threats tracking this CVE

• SHADOW-EARTH-053 — China-Aligned Cyberespionage Campaign Exploiting Microsoft Exchange (ProxyLogon CVE-2021-26855/26857/26858/27065) and IIS to Deploy GODZILLA Web Shells and ShadowPad — HIGH
• UAT-8099 (China) BadIIS Malware Campaign Targeting IIS Servers for SEO Fraud — HIGH

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858
• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858
• https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858

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Enriched from CVE.org, NVD (this product uses the NVD API but is not endorsed or certified by the NVD), FIRST EPSS, CISA KEV, and GitHub Security Advisories.