CVE-2021-31207
Microsoft Exchange Server 2013 … 2019
Raw vector
CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2021-31207 is a medium-severity Unrestricted Upload of File with Dangerous Type (CWE-434) vulnerability in Microsoft Exchange Server. Its CVSS base score is 6.6 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked in the top 0.0% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2021-31207 is a security feature bypass vulnerability affecting Microsoft Exchange Server and tracked under CWE-434 for unrestricted upload of files with dangerous types. It carries a CVSS 3.1 score of 6.6 with a vector indicating network attack vector, high attack complexity, and high privileges required.
An attacker who can reach the server over the network and satisfies the high complexity precondition may bypass security controls to achieve high impact on confidentiality, integrity, and availability. Public references associate the issue with the ProxyShell remote code execution chain.
Microsoft Security Response Center advisory CVE-2021-31207 and the corresponding Zero Day Initiative advisory ZDI-21-819 describe the vulnerability and outline available patches or configuration guidance for affected Exchange deployments.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2021-18120
Vulnerability Data
Microsoft Exchange Server Security Feature Bypass Vulnerability
- CWE(s)
- KEV Date Added
- 03 November 2021
Related Threats
Threat-Actor AttributionAI
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V5.1.1
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Requiring identifiable owners for portable devices reduces the attack surface for unrestricted uploads of dangerous file types via anonymous media.
Dangerous file uploads can be detonated in the chamber to determine malice before any production write or execution occurs.
Prevents unrestricted writing of arbitrary or malicious firmware by keeping hardware write-protect enabled except under tightly controlled manual procedures.
Scans files from external sources on download/open/execute, blocking unrestricted uploads of dangerous file types.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Hardened configuration baselines can enforce allowed file types and processing rules.
Restricting execution of unauthorized software directly blocks dangerous uploaded files from running.
Secure development practices include input validation and file-type restrictions that prevent this weakness.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.