CVE-2021-31207
MEDIUM
Unrestricted Upload of File with Dangerous Type (CWE-434)
2021-05-11
secure@microsoft.com
6.6
CVSS 3.1
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CVSS VectorNVD
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
Attack Vector
Network
Attack Complexity
High
Privileges Required
High
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High
Lifecycle Timeline
5
Analysis Generated
Mar 26, 2026 - 11:19 vuln.today
Added to CISA KEV
Oct 30, 2025 - 19:40 cisa
CISA KEV
PoC Detected
Oct 30, 2025 - 19:40 vuln.today
Public exploit code
Patch released
Oct 30, 2025 - 19:40 nvd
Patch available
CVE Published
May 11, 2021 - 19:15 nvd
MEDIUM 6.6
DescriptionNVD
Microsoft Exchange Server Security Feature Bypass Vulnerability
Analysis
Microsoft Exchange Server Security Feature Bypass Vulnerability
Technical ContextAI
Unrestricted file upload allows attackers to upload malicious files (web shells, executables) that can then be executed on the server. This vulnerability is classified as Unrestricted Upload of File with Dangerous Type (CWE-434).
RemediationAI
A vendor patch is available — apply it immediately. Validate file types by content (magic bytes), not just extension. Store uploads outside the web root. Use random filenames. Scan uploads for malware.
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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).