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CVE-2021-39214

31
FAUCET Score

CVE-2021-39214 describes an HTTP request smuggling vulnerability in mitmproxy versions 7.0.2 and below, allowing malicious clients or servers to bypass security controls. This critical vulnerability, rated 9.8 CVSS, enables attackers to smuggle requests or responses within legitimate HTTP messages, circumventing mitmproxy's event hooks and potentially access controls or input sanitization. While no active exploitation or public exploit code is currently reported, the vulnerability has garnered significant community discussion. Organizations using mitmproxy to protect HTTP/1 services should upgrade to version 7.0.3 or higher immediately.

Impacted Technologies

VendorProductVersion(s)CPE
<= 7.0.2CPE matchmatch criteria
cpe:2.3:a:mitmproxy:mitmproxy:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

8.1HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
2.2
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.18%
Probability of exploitation in next 30 days
EPSS Percentile
64.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0118 is in the 50th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (1)

pippatch availablevia ghsa
Product: mitmproxyFixed in: 7.0.3

Vendor Advisories (1)

pipGHSA-22gh-3r9q-xf38critical

Lacking Protection against HTTP Request Smuggling in mitmproxy

Sep 20, 2021

References

github.com / mitmproxy/mitmproxy/security/advisories/GHSA-22gh-3r9q-xf38
Third Party Advisory