CVE-2021-26857

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: 97.4%
KEV: ⚠ Exploited

Published

March 3, 2021

Last Modified

December 18, 2025

Advisory Details (2)

Auto-updated Jun 3, 2026

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

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-2021-26857

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-2021-26857

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

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-2021-268572021-03-02
Microsoft Exchange Server Remote Code Execution Vulnerability

Data Freshness Timeline

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

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-03 16:30 UTCEG score recompute
2026-06-03 16:30 UTCVendor advisory
2026-06-03 16:30 UTCGHSA enrichment
2026-06-03 12:12 UTCEG score recompute
2026-06-03 12:12 UTCVendor advisory
2026-06-03 12:12 UTCGHSA enrichment
2026-06-03 07:54 UTCEG score recompute
2026-06-03 07:54 UTCVendor advisory
2026-06-03 07:54 UTCGHSA enrichment
2026-06-03 03:36 UTCEG score recompute
2026-06-03 03:36 UTCVendor advisory
2026-06-03 03:36 UTCGHSA enrichment
2026-06-02 23:18 UTCEG score recompute
2026-06-02 23:18 UTCVendor advisory
2026-06-02 23:18 UTCGHSA enrichment
2026-06-02 20:11 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-02 19:00 UTCEG score recompute
2026-06-02 19:00 UTCVendor advisory

Publicly available exploits

(1 reference)

Working exploit code is in the public domain (1 GitHub PoC). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

GitHub PoCsirpedrotavares/Proxylogon-exploit
First seen Mar 11, 2021
proxylogon exploit - CVE-2021-26857
Open source ↗

Frequently asked(6)

What is CVE-2021-26857?

CVE-2021-26857 is a high vulnerability published on March 3, 2021. Microsoft Exchange Server Remote Code Execution Vulnerability

When was CVE-2021-26857 disclosed?

CVE-2021-26857 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-2021-26857 actively exploited?

Yes. CISA added CVE-2021-26857 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-2021-26857?

CVE-2021-26857 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-2021-26857?

CVE-2021-26857 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-2021-26857?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-26857, 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-2021-26857

Explore →

Is Your Infrastructure Affected by CVE-2021-26857?

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CVE-2021-26857

Published

Last Modified

Advisory Details (2)

Known Exploited Vulnerabilities Catalog | CISA

Security Update Guide - Microsoft Security Response Center

Weakness Classification(2)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

Frequently asked(6)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-26857?

Same vendor

Same CWE

CVE-2021-26857

📅 Published

🔄 Last Modified

📋 Advisory Details (2)

Known Exploited Vulnerabilities Catalog | CISA

Security Update Guide - Microsoft Security Response Center

Weakness Classification(2)

All Vendor Advisories

Data Freshness Timeline

Publicly available exploits

❓ Frequently asked(6)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-26857?

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Published

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Advisory Details (2)

Frequently asked(6)

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