Is CVE-2021-39214 actively exploited?

No active exploitation of CVE-2021-39214 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-39214 be exploited remotely?

Yes. CVE-2021-39214 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-39214?

CVE-2021-39214 has a CVSS score of 9.8 (CRITICAL).

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CRITICAL

CVE-2021-39214

CWE-444Published: September 16, 2021· Updated: Jun 17, 2026

9.8

CVSS v3.1

Official Description

mitmproxy is an interactive, SSL/TLS-capable intercepting proxy. In mitmproxy 7.0.2 and below, a malicious client or server is able to perform HTTP request smuggling attacks through mitmproxy. This means that a malicious client/server could smuggle a request/response through mitmproxy as part of another request/response's HTTP message body. While a smuggled request is still captured as part of another request's body, it does not appear in the request list and does not go through the usual mitmproxy event hooks, where users may have implemented custom access control checks or input sanitization. Unless one uses mitmproxy to protect an HTTP/1 service, no action is required. The vulnerability has been fixed in mitmproxy 7.0.3 and above.

NVD Source

Technical Analysis

CVE-2021-39214 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in complete confidentiality breach (data exposure), full integrity compromise (data manipulation), availability disruption (denial of service), with a CVSS base score of 9.8.