What is the CVSS score of CVE-2021-31207?

CVE-2021-31207 has a CVSS 3.1 base score of 6.6 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 93.8%.

Is there a public PoC exploit available for CVE-2021-31207?

Yes, a public proof-of-concept exploit is available for CVE-2021-31207. Prioritise patching immediately. EPSS: 93.8%.

How to fix or mitigate CVE-2021-31207?

Within 24 hours: Identify affected systems and apply vendor patches immediately. Review file handling controls.

CVE-2021-31207

MEDIUM

Unrestricted Upload of File with Dangerous Type (CWE-434)

2021-05-11 secure@microsoft.com

6.6

CVSS 3.1 · NVD

View

Vulnerability Assessment

Weakness	CWE CWE-434 OWASP Top 10:2025 A04:2021 - Insecure Design ASVS 5.0 V1 - Architecture, Design and Threat Modeling Secure design patterns, threat modeling MITRE ATT&CK 2 techniques across 2 tactics: Command and Control, Persistence The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	Remote code execution through uploaded web shells or malware, leading to complete server compromise. With a CVSS score of 6.6 (MEDIUM), this represents a moderate risk. This vulnerability is listed in the CISA Known Exploited Vulnerabilities catalog, indicating active exploitation in the wild. Public exploit code is available, increasing the likelihood of exploitation.
Exploit ScenarioDerived	An attacker uploads a PHP/JSP web shell disguised with a legitimate extension, then accesses it via the web server to execute arbitrary commands.

Act Now Prioritize within 24-48h. Why: In CISA KEV with patch available.

Exploited in the wild (CISA KEV) Patch available 93.8% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 26, 2026

Microsoft Exchange Server Security Feature Bypass Vulnerability

Earlier versions of this analysis (1)

v1 Mar 26, 2026 - 11:19 CVSS 6.6

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.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

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).

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 6.6 MEDIUM

AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

High

Privileges Required

High

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

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

Executive ViewAI

Why It Matters

CVE-2021-31207 presents notable security risk, a unrestricted file upload vulnerability rated CVSS 6.6. This could allow unauthorized file access. This vulnerability is actively exploited in the wild (KEV-listed). A patch is available and should be applied during regular vulnerability management.

Business Impact: High

Compensating Controls

Apply vendor patch. If patching is delayed: restrict file access via WAF, implement allowlists.

Threat Intelligence Overview

Threat Score

9.1/10

Composite threat intelligence

EPSS Score

93.8%

Top 0% exploitable

Threat Intel

1 sources

Exploit

POC

Public exploit code exists

Data Quality

6 sources

Confidence: High

NVD

CVE.org

CISA KEV

EPSS POC (1) THREAT

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV Yes

Public POC Yes

EPSS 93.8%

Patch available Yes

Active threat Yes

Deciding rule

In CISA KEV with patch available

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.