Is CVE-2021-40377 actively exploited?

No active exploitation of CVE-2021-40377 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-40377 be exploited remotely?

Yes. CVE-2021-40377 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-40377?

CVE-2021-40377 has a CVSS score of 5.4 (MEDIUM).

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MEDIUM

CVE-2021-40377

CWE-79Published: September 8, 2021· Updated: Jun 17, 2026

5.4

CVSS v3.1

Official Description

SmarterTools SmarterMail 16.x before build 7866 has stored XSS. The application fails to sanitize email content, thus allowing one to inject HTML and/or JavaScript into a page that will then be processed and stored by the application.

NVD Source

Technical Analysis

CVE-2021-40377 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

Exploitation requires low privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

The vulnerability has a "Changed" scope, meaning successful exploitation can impact components beyond the vulnerable component itself — such as the host operating system or adjacent services.

From a weakness classification perspective (CWE-79): Cross-site scripting (XSS) vulnerabilities allow attackers to inject malicious scripts into web pages viewed by other users.