CVE-2021-26858

HIGHNVD 7.89.0▲Trending — 5 sources updated this weekExploited in the wild

7.8

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3: 7.8
EG Score: 9.0(high)
EPSS: 98.8%
KEV: ⚠ Exploited

Published

March 3, 2021

Last Modified

December 18, 2025

Advisory Details (2)

Auto-updated Jun 4, 2026

⚠️ Active exploitation confirmed. Patch available. Sources: microsoft, cisa.

cisa Patch Available🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26858

microsoft Patch Available

Security Update Guide - Microsoft Security Response Center

Security Update Guide - Microsoft Security Response Center. Patch available via Microsoft Security Update

https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Microsoft MSRCCVE-2021-268582021-03-02
Microsoft Exchange Server Remote Code Execution Vulnerability

Data Freshness Timeline

(refreshed 20× in last 7d / 20× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

2026-06-10 03:36 UTCEG score recompute
2026-06-10 03:36 UTCVendor advisory
2026-06-10 03:36 UTCGHSA enrichment
2026-06-09 23:28 UTCEG score recompute
2026-06-09 23:28 UTCVendor advisory
2026-06-09 23:28 UTCGHSA enrichment
2026-06-09 19:19 UTCEG score recompute
2026-06-09 19:19 UTCVendor advisory
2026-06-09 19:19 UTCGHSA enrichment
2026-06-09 18:42 UTCCISA KEV update
2026-06-09 17:12 UTCCISA KEV update
2026-06-09 15:11 UTCEG score recompute
2026-06-09 15:11 UTCVendor advisory
2026-06-09 15:11 UTCGHSA enrichment
2026-06-09 11:03 UTCEG score recompute
2026-06-09 11:03 UTCVendor advisory
2026-06-09 11:03 UTCGHSA enrichment
2026-06-09 06:55 UTCEG score recompute
2026-06-09 06:55 UTCVendor advisory
2026-06-09 06:55 UTCGHSA enrichment

Frequently asked(6)

What is CVE-2021-26858?

CVE-2021-26858 is a high vulnerability published on March 3, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability

When was CVE-2021-26858 disclosed?

CVE-2021-26858 was first published in the National Vulnerability Database on March 3, 2021, with the most recent update on December 18, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-26858 actively exploited?

Yes. CISA added CVE-2021-26858 to the Known Exploited Vulnerabilities catalog on November 3, 2021, affecting Microsoft Exchange Server. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate patching attention.

What is the CVSS score of CVE-2021-26858?

CVE-2021-26858 has a CVSS v3 base score of 7.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 9.0.

Which products are affected by CVE-2021-26858?

CVE-2021-26858 affects Microsoft Exchange Server. The full affected-products list, including version ranges and fixed versions, is shown in the Affected Packages section of this page.

How do I remediate CVE-2021-26858?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-26858, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-26858

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