CVE-2021-26858
HIGH
2021-03-03
secure@microsoft.com
7.8
CVSS 3.1
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CVSS VectorNVD
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Attack Vector
Local
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Lifecycle Timeline
4
Analysis Generated
Mar 26, 2026 - 11:19 vuln.today
Added to CISA KEV
Dec 18, 2025 - 02:00 cisa
CISA KEV
Patch released
Dec 18, 2025 - 02:00 nvd
Patch available
CVE Published
Mar 03, 2021 - 00:15 nvd
HIGH 7.8
DescriptionNVD
Microsoft Exchange Server Remote Code Execution Vulnerability
AnalysisAI
Microsoft Exchange Server allows authenticated attackers to write arbitrary files to the server filesystem, the third component of the ProxyLogon exploit chain enabling web shell deployment.
Technical ContextAI
The post-authentication file write vulnerability allows writing arbitrary content to any filesystem location accessible by the Exchange service account (SYSTEM). Combined with the SSRF (CVE-2021-26855) for authentication bypass, this enables unauthenticated web shell deployment.
Affected ProductsAI
Microsoft Exchange Server 2013/2016/2019
RemediationAI
Apply security updates. Scan for web shells in Exchange web directories. Monitor file creation events in IIS content directories.
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External POC / Exploit Code
Leaving vuln.today
Destination URL
POC code from unknown sources may be malicious, contain backdoors, or be fake.
Always review and test exploit code in a safe, isolated environment (VM/sandbox).
Verify the source reputation and cross-reference with known databases (Exploit-DB, GitHub Security).