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Fencer Intel
high 8.1

CVE-2021-39214 json

Lacking Protection against HTTP Request Smuggling in mitmproxy

published 5y ago modified 4mo ago also GHSA-22gh-3r9q-xf38 , PYSEC-2021-328 , EUVD-2021-0135

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.1%
EPSS 1.1% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi mitmproxy 7.0.3
  • mitmproxy Debian 14, Debian 12 8.1.1-1

debian advisories DEBIAN-CVE-2021-39214

  • python-mitmproxy Package Hub 15 SP5, openSUSE Leap 15.5 3.0.4-bp155.3.3.1
  • python-mitmproxy Package Hub 15 SP4, openSUSE Leap 15.4 3.0.4-bp154.2.3.1

opensuse advisories openSUSE-SU-2023:0233-1openSUSE-SU-2023:0232-1

  • mitmproxy Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 7.0.3-r0

alpine advisories ALPINE-CVE-2021-39214

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • mitmproxy Arch Linux 7.0.3-1

arch linux advisories AVG-2395

Is CVE-2021-39214 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Exploit prediction

1.06% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
GitHub 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
pypi mitmproxy
<7.0.3
7.0.3

Affected products

  • mitmproxy mitmproxy

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.