CVE-2021-39214

Lacking Protection against HTTP Request Smuggling in mitmproxy

CRITICAL
9.8
CVSS Score
Published: September 16, 2021 at 03:10 PM UTC
Updated: June 17, 2026 at 04:03 AM UTC
1 product affected across 1 vendorMitmproxy

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Severity
CRITICAL9.8
Exploit prediction
EPSS 1%

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v ≤ 7.0.2
Affected range stops below 7.0.3, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
HIGH
Availability
HIGH
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-444

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