Search/CVE-2021-26855
● CVE — Critical

CVE-2021-26855

VendormicrosoftProductexchange serverDiscoveredMar 3, 2021UpdatedAug 19, 2026

Microsoft Exchange Server Remote Code Execution Vulnerability

CVSS v3.1
9.1 CRITICAL
EPSS
99.9%
probability of exploitation in 30 days
CISA KEV
Listed
confirmed active exploitation
News coverage
21
sources referencing this CVE
Related IOCs
seen in the same coverage
EPSS Trend
Aug 16, 2026 → Aug 21, 2026
● 0.00pp
99.9% → 99.9% over 2 tracked changes
CVSS v3.1 Detail
Attack VectorNETWORK
Attack ComplexityLOW
Privileges RequiredNONE
User InteractionNONE
ScopeUNCHANGED
ConfidentialityHIGH
IntegrityHIGH
AvailabilityNONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Connections
26 relationships
Timeline
disclosure → media coverage
Mar 3, 2021
Disclosure — published as a CVE record. · last revised by NVD Aug 19, 2026
Jul 22, 2025
thehackernews.com reports: Microsoft Links Ongoing SharePoint Exploits to Three Chinese Hacker Groups
Jul 25, 2025
securelist.com reports: ToolShell: a story of five vulnerabilities in Microsoft SharePoint
Jul 30, 2025
thehackernews.com reports: Chinese Firms Linked to Silk Typhoon Filed 15+ Patents for Cyber Espionage Tools
Jul 30, 2025
therecord.media reports: Patents by Silk Typhoon-linked company shed light on Beijing’s offensive hacking capabilities
Aug 7, 2025
bleepingcomputer.com reports: Microsoft warns of high-severity flaw in hybrid Exchange deployments
Aug 22, 2025
bleepingcomputer.com reports: Murky Panda hackers exploit cloud trust to hack downstream customers
Sep 30, 2025
thehackernews.com reports: Phantom Taurus: New China-Linked Hacker Group Hits Governments With Stealth Malware
Oct 30, 2025
bleepingcomputer.com reports: CISA and NSA share tips on securing Microsoft Exchange servers
Nov 7, 2025
bleepingcomputer.com reports: U.S. Congressional Budget Office hit by suspected foreign cyberattack
Nov 7, 2025
thehackernews.com reports: From Log4j to IIS, China’s Hackers Turn Legacy Bugs into Global Espionage Tools
Apr 30, 2026
go.theregister.com reports: What type of 'C2 on a sleep cycle' do they leave behind? Novel Chinese spy group found in critical networks in Poland, Asia
May 1, 2026
thehackernews.com reports: China-Linked Hackers Target Asian Governments, NATO State, Journalists, and Activists
May 15, 2026
bleepingcomputer.com reports: Microsoft warns of Exchange zero-day flaw exploited in attacks
May 21, 2026
thehackernews.com reports: Showboat Linux Malware Hits Middle East Telecom with SOCKS5 Proxy Backdoor
Jun 24, 2026
securelist.com reports: StrikeShark: investigating a new campaign delivering Cobalt Strike through SharkLoader
Jun 26, 2026
thehackernews.com reports: New SharkLoader Malware Deploys Cobalt Strike in StrikeShark Cyberattacks
Sep 4, 2026
cybersecurity360.it reports: Server Exchange, cinque scudi per la posta elettronica
Sep 16, 2026
thehackernews.com reports: Three Threat Groups Target Russian Enterprises With Backdoors, Ransomware, and Wipers
Sep 17, 2026
welivesecurity.com reports: Beware the SparroWock: The backdoor that bites, the commands that catch
Sep 17, 2026
infosecurity-magazine.com reports: FamousSparrow Swaps SparrowDoor For New SparroWocky Backdoor
Oct 8, 2026
thehackernews.com reports: U.S. Offers Up to $10 Million for Tips on Zhang Yu, Charged in HAFNIUM Hacks