CVE-2021-27065
Published: 03 March 2021
Summary
CVE-2021-27065 is a high-severity Path Traversal (CWE-22) vulnerability in Microsoft Exchange Server. Its CVSS base score is 7.8 (High).
Operationally, 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.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2021-27065 is a remote code execution vulnerability in Microsoft Exchange Server that is associated with CWE-22 path traversal. The flaw received a CVSS v3.1 base score of 7.8 with the vector string AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, indicating local attack vector, no required privileges, and required user interaction to reach full confidentiality, integrity, and availability impact.
An attacker who can reach the affected Exchange component may leverage the vulnerability to execute arbitrary code on the server. Public proof-of-concept material referencing the ProxyLogon exploitation chain has been posted to PacketStorm Security, confirming that working artifacts exist for this issue.
Microsoft published an advisory for CVE-2021-27065 on its security guidance portal that addresses the vulnerability and associated patches.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2021-13836
Vulnerability details
Microsoft Exchange Server Remote Code Execution Vulnerability
- CWE(s)
- KEV Date Added
- 03 November 2021
Related Threats
Threat-Actor AttributionAI
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Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely application of vendor patches that Microsoft released to eliminate the path-traversal flaw in Exchange.
Enforces validation of user-supplied input to block the path-traversal sequences that enable arbitrary code execution.
Requires integrity verification of Exchange binaries and configuration files to detect unauthorized modifications resulting from successful exploitation.