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CVE-2021-27065

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS 7.8 (HIGH) KEV: KNOWN CATALOG

Attention and evidence

HYPE SCORE
0.0/10
REALITY · THREAT PRIORITY
8.7/10
General review priority; not probability

Evidence confidence: Exploitation recorded

Why this priority?
  • Recorded exploitation baseline: +7.00
  • Technical severity: CVSS 7.8: +1.17
  • Fresh EPSS: 99.88%: +0.50

General review priority, not probability, victim count or asset-specific risk. A range covers missing CVSS/EPSS inputs within the current evidence state.

Sources: 16 documents and public datasets.

Hype components

Headline sample (25%)
0/100
Press, 30 days (60%)
0/100
Grounded branding (15%)
0/100
HYPE TOTAL0/100

Sources and documents

Barracuda Networks Blog
Press · 09 Dec 2025, 08:00 · Barracuda detects increased probing for Microsoft Exchange vulnerabilities - Barracuda Networks Blog
Barracuda Blog
Press · 05 Dec 2025, 08:00 · Cybersecurity Threat Advisory: Global Microsoft Exchange attack - Barracuda Blog
SECURITY.COM
Press · 06 Oct 2024, 21:13 · How Symantec Stops Microsoft Exchange Server Attacks - SECURITY.COM
Qualys
Press · 06 May 2022, 07:00 · CISA Alert: Top 15 Routinely Exploited Vulnerabilities - Qualys
Qualys
Press · 28 Jul 2021, 07:00 · CISA Alert: Top Routinely Exploited Vulnerabilities - Qualys
See all 16 source documents
SECURITY.COM
Press · 29 Mar 2021, 07:00 · Symantec Data Center Security Provides Zero Day Protection - SECURITY.COM
Rapid7
Press · 26 Mar 2021, 07:00 · Metasploit Wrap-Up: 3/26/21 - Rapid7
Recorded Future
Press · 25 Mar 2021, 07:00 · Suspected Chinese Group Calypso APT Exploiting Vulnerable Microsoft Exchange Servers - Recorded Future
Sophos
Press · 17 Mar 2021, 07:00 · MTR in Real-Time: Exchange ProxyLogon Edition - Sophos
WeLiveSecurity
Press · 10 Mar 2021, 08:00 · Exchange servers under siege from at least 10 APT groups - WeLiveSecurity
Cloudflare Blog
Press · 07 Mar 2021, 08:00 · Protecting against recently disclosed Microsoft Exchange Server vulnerabilities: CVE-2021-26855, CVE-2021-26857, CVE-2021-26858, and CVE-2021-27065 - Cloudflare Blog
Cisco Talos Blog
Press · 04 Mar 2021, 08:00 · Threat Advisory: HAFNIUM and Microsoft Exchange zero-day - Cisco Talos Blog
Qualys
Press · 03 Mar 2021, 08:00 · Microsoft Exchange Server Zero-Days (ProxyLogon) – Automatically Discover, Prioritize and Remediate Using Qualys VMDR - Qualys
Krebs on Security
Press · 02 Mar 2021, 08:00 · Microsoft: Chinese Cyberspies Used 4 Exchange Server Flaws to Plunder Emails - Krebs on Security
Microsoft
Press · 02 Mar 2021, 08:00 · HAFNIUM targeting Exchange Servers with 0-day exploits - Microsoft
The Record from Recorded Future News
Press · 01 Mar 2021, 08:00 · Microsoft: Chinese APT Targeted Exchange Servers With Four Zero-Days - The Record from Recorded Future News

Score evolution

● Hype   ● Reality

Earlier evidence-support scores are retained in history; this chart shows only the current priority definition.

First record: hype 0.0 · reality 8.7 (2026-11-02 15:12). The curve appears once the score changes.

Public exploit evidence

1

Public exploit entries / repo candidates

See 1 repos with metrics
RepositoryStarsForksLanguageUpdated
herwonowr/exprolog18539Python19 Oct 2021, 07:07
Public exploit evidence
Evidence context and dated references

Reality is general threat/review priority, combining observed exploitation, CVSS severity and fresh EPSS. Evidence confidence is separate. This is not calibrated risk, a victim count or an asset-specific assessment. A range reflects missing numeric inputs.

Evidence in context

Confidence in exploitation evidence
Exploitation recorded
Priority basis
Recorded exploitation; CVSS 7.8; EPSS 99.9%
Attention, last 30 days
0 distinct story titles; 0 press documents; 0 publisher domains.
Technical potential
local access, no prior privileges, user interaction.
Observed activity
Exploitation recorded in CISA KEV.
Known scale
Not quantified.
Evidence confidence basis
Trusted exploitation confirmation

Score evaluated: 2026-11-05 13:58:25.853394+00:00 · EPSS snapshot: 2026-11-05T12:03:04Z

Source event timeline
First press mention
01 Mar 2021, 08:00
Published
02 Mar 2021, 23:55
Added to the CISA KEV catalog
03 Nov 2021, 00:00
Latest press mention
09 Dec 2025, 08:00
Score calculated
05 Nov 2026, 13:58
PoCs on GitHub
1 repositories
Source: CVE List V5 · CISA KEV · FIRST EPSS · GitHub · RSSVulnRadar