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CVE-2021-34473

ProxyShell

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS 9.1 (CRITICAL) KEV: KNOWN CATALOG

Attention and evidence

HYPE SCORE
0.0/10
REALITY · THREAT PRIORITY
8.9/10
General review priority; not probability

Evidence confidence: Exploitation recorded

Why this priority?
  • Recorded exploitation baseline: +7.00
  • Technical severity: CVSS 9.1: +1.36
  • Fresh EPSS: 100.00%: +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: 32 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 Blog
Press · 05 Dec 2025, 08:00 · Cybersecurity Threat Advisory: Global Microsoft Exchange attack - Barracuda Blog
Help Net Security
Press · 17 Jun 2025, 07:00 · Researchers unearth keyloggers on Outlook login pages - Help Net Security
SC Media
Press · 31 Jul 2024, 07:00 · UK electoral agency cyberattack prompted by security failings - SC Media
SC Media
Press · 09 Jan 2024, 08:00 · ProxyShell-targeting Babuk Tortilla ransomware decrypted after hacker’s arrest - SC Media
SOCRadar
Press · 06 Feb 2023, 08:00 · Microsoft Exchange Server Flaw Trend in 2022 - SOCRadar
See all 32 source documents
Securelist
Press · 19 Dec 2022, 08:00 · CVE-2022-41040 and CVE-2022-41082 – zero-days in MS Exchange - Securelist
thezdi.com
Press · 16 Nov 2022, 08:00 · Control Your Types or Get Pwned: Remote Code Execution in Exchange PowerShell Backend - thezdi.com
www.trendmicro.com
Press · 25 Oct 2022, 07:00 · LV Ransomware Exploits ProxyShell in Attack on a Jordan-based Company - www.trendmicro.com
DoublePulsar
Press · 29 Sep 2022, 07:00 · ProxyNotShell— the story of the claimed zero days in Microsoft Exchange - DoublePulsar
Qualys
Press · 06 May 2022, 07:00 · CISA Alert: Top 15 Routinely Exploited Vulnerabilities - Qualys
Sophos
Press · 28 Feb 2022, 08:00 · Conti and Karma actors attack healthcare provider at same time through ProxyShell exploits - Sophos
TechTarget
Press · 29 Dec 2021, 08:00 · Everything you need to know about ProxyShell vulnerabilities - TechTarget
TechTarget
Press · 29 Dec 2021, 08:00 · Everything you need to know about ProxyShell vulnerabilities - TechTarget
TechTarget
Press · 01 Dec 2021, 08:00 · BlackByte ransomware attacks exploiting ProxyShell flaws - TechTarget
TechTarget
Press · 29 Nov 2021, 08:00 · ProxyShell vs. ProxyLogon: What’s the difference? - TechTarget
www.trendmicro.com
Press · 19 Nov 2021, 08:00 · Squirrelwaffle Exploits ProxyShell and ProxyLogon to Hijack Email Chains - www.trendmicro.com
Google Cloud
Press · 17 Nov 2021, 08:00 · ProxyNoShell: A Change in Tactics Exploiting ProxyShell Vulnerabilities - Google Cloud
www.trendmicro.com
Press · 17 Nov 2021, 08:00 · Analyzing ProxyShell-related Incidents via Trend Micro Managed XDR - www.trendmicro.com
TechTarget
Press · 15 Nov 2021, 08:00 · ProxyShell leads to domain-wide ransomware attack - TechTarget
BleepingComputer
Press · 04 Nov 2021, 07:00 · Microsoft Exchange ProxyShell exploits used to deploy Babuk ransomware - BleepingComputer
BleepingComputer
Press · 03 Sep 2021, 07:00 · Conti ransomware now hacking Exchange servers with ProxyShell exploits - BleepingComputer
Security Affairs
Press · 03 Sep 2021, 07:00 · Conti ransomware gang targets Microsoft Exchange servers with ProxyShell exploits - Security Affairs
Google Cloud
Press · 02 Sep 2021, 07:00 · PST, Want a Shell? ProxyShell Exploiting Microsoft Exchange Servers - Google Cloud
Huntress
Press · 26 Aug 2021, 07:00 · ProxyShell vs. ProxyLogon: What's the Difference? - Huntress
Cybersecurity Dive
Press · 24 Aug 2021, 07:00 · Microsoft Exchange vulnerabilities targeted in ProxyShell attacks - Cybersecurity Dive
Sophos
Press · 23 Aug 2021, 07:00 · ProxyShell vulnerabilities in Microsoft Exchange: What to do - Sophos
TechTarget
Press · 23 Aug 2021, 07:00 · CISA: ProxyShell flaws being actively exploited, patch now - TechTarget
thezdi.com
Press · 18 Aug 2021, 07:00 · From Pwn2Own 2021: A New Attack Surface on Microsoft Exchange - ProxyShell! - thezdi.com
TechTarget
Press · 17 Aug 2021, 07:00 · Many Exchange servers still vulnerable to ProxyLogon, ProxyShell - TechTarget
Rapid7
Press · 12 Aug 2021, 07:00 · ProxyShell: More Widespread Exploitation of Microsoft Exchange Servers - Rapid7
SOC Prime
Press · 10 Aug 2021, 07:00 · Microsoft Exchange ProxyShell Attack Detection - SOC Prime
TechTarget
Press · 09 Aug 2021, 07:00 · ‘ProxyShell’ Exchange bugs resurface after presentation - TechTarget

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 8.9 (2026-11-02 15:12). The curve appears once the score changes.

Public exploit evidence

2

Public exploit entries / repo candidates

See 2 repos with metrics
RepositoryStarsForksLanguageUpdated
psc4re/NSE-scripts16227Lua16 Aug 2021, 18:16
mithridates1313/ProxyShell_POC165Python06 Oct 2021, 11:35
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 9.1; EPSS 100.0%
Attention, last 30 days
0 distinct story titles; 0 press documents; 0 publisher domains.
Technical potential
network access, no prior privileges, no user interaction.
Observed activity
Exploitation recorded in CISA KEV.
Known scale
Not quantified.
Evidence confidence basis
Trusted exploitation confirmation

Score evaluated: 2026-11-05 13:58:27.921902+00:00 · EPSS snapshot: 2026-11-05T12:03:04Z

Source event timeline
Published
14 Jul 2021, 17:54
First press mention
09 Aug 2021, 07:00
Added to the CISA KEV catalog
03 Nov 2021, 00:00
Latest press mention
05 Dec 2025, 08:00
Score calculated
05 Nov 2026, 13:58
Name
ProxyShell
PoCs on GitHub
2 repositories
Source: CVE List V5 · CISA KEV · FIRST EPSS · GitHub · RSSVulnRadar