GHSA-63cx-g855-hvv4: Mitmproxy Mitmproxy Binaries Embed A Vulnerable Vulnerability

MODERATE
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CWE-1395 CWE-444
Published
Advisory Summary

GHSA-63cx-g855-hvv4 is a MODERATE mitmproxy binaries embed a vulnerable vulnerability (CWE-1395: Dependency on Vulnerable Third-Party Component) affecting Mitmproxy libraries in the PyPI ecosystem. The issue involves mitmproxy binaries embed a vulnerable python-hyper/h2 dependency. Remediation is available by upgrading affected packages to version 12.1.2.

GHSA-63cx-g855-hvv4 at a Glance

CVE Identifier N/A
GHSA Identifier GHSA-63cx-g855-hvv4
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-1395: Dependency on Vulnerable Third-Party Component
Affected Product Mitmproxy
Package Ecosystem PyPI
Published Date
Last Updated

How to Fix GHSA-63cx-g855-hvv4

To remediate this vulnerability, upgrade all affected Mitmproxy dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

mitmproxy fixed: 12.1.2 
pip install mitmproxy>=12.1.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show mitmproxy

How to Check if You Are Affected

To determine whether your Python environment is affected by GHSA-63cx-g855-hvv4, inspect your installed packages using pip:

pip show mitmproxy

Analyze the terminal output to locate any version of Mitmproxy in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 12.1.2), your application is affected.

Note: The pip show mitmproxy command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-1395: Dependency on Vulnerable Third-Party Component, where the product has a dependency on a third-party component that contains one or more known vulnerabilities. In Mitmproxy, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

mitmproxy 12.1.1 and below embed python-hyper/h2 ≤ v4.2.0, which has a gap in its HTTP/2 header validation. This enables request smuggling attacks when mitmproxy is in a configuration where it translates HTTP/2 to HTTP/1. For example, this affects reverse proxies to `http://` backends. It does not affect mitmproxy's regular mode. All users are encouraged to upgrade to mitmproxy 12.1.2, which includes a fixed version of h2. More details about the vulnerability itself can be found at https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h.

GHSA-63cx-g855-hvv4 Affected Mitmproxy Versions

1 component(s)
Fixed Versions:
12.1.2
Product / Package Ecosystem Affected Versions Fixed Version
mitmproxy
pypi/mitmproxy
PyPI
< 12.1.2
12.1.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/mitmproxy/mitmproxy/security/advisories/GHSA-63cx-g855-hvv4
GitHub Advisory / Wiki ADVISORY
https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h
Mitmproxy Source Repository REPOSITORY
https://github.com/mitmproxy/mitmproxy

Frequently Asked Questions

What is GHSA-63cx-g855-hvv4?
GHSA-63cx-g855-hvv4 is a security vulnerability in Mitmproxy involving mitmproxy binaries embed a vulnerable python-hyper/h2 dependency under CWE-1395: Dependency on Vulnerable Third-Party Component.
Which Mitmproxy versions are affected?
Affected versions include releases prior to 12.1.2 across affected packages: mitmproxy.
What version fixes GHSA-63cx-g855-hvv4?
Upgrading to 12.1.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is mitmproxy affected?
Yes, mitmproxy is affected in releases prior to 12.1.2. Upgrade your dependency to 12.1.2 or later.
What CWE is associated with GHSA-63cx-g855-hvv4?
GHSA-63cx-g855-hvv4 is classified under CWE-1395: Dependency on Vulnerable Third-Party Component (The product has a dependency on a third-party component that contains one or more known vulnerabilities.).
How can I check PyPI dependencies for GHSA-63cx-g855-hvv4?
Run the dependency tree command: 'pip show mitmproxy'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-63cx-g855-hvv4",
  "modified" : "2025-08-25T21:01:01Z",
  "published" : "2025-08-25T21:01:00Z",
  "aliases" : [ ],
  "summary" : "mitmproxy binaries embed a vulnerable python-hyper/h2 dependency",
  "details" : "mitmproxy 12.1.1 and below embed python-hyper/h2 ≤ v4.2.0, which has a gap in its HTTP/2 header validation. This enables request smuggling attacks when mitmproxy is in a configuration where it translates HTTP/2 to HTTP/1. For example, this affects reverse proxies to `http://` backends. It does not affect mitmproxy's regular mode.\n\nAll users are encouraged to upgrade to mitmproxy 12.1.2, which includes a fixed version of h2.\n\nMore details about the vulnerability itself can be found at https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "mitmproxy"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "12.1.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 12.1.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mitmproxy/mitmproxy/security/advisories/GHSA-63cx-g855-hvv4"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mitmproxy/mitmproxy"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1395", "CWE-444" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-08-25T21:01:00Z",
    "nvd_published_at" : null
  }
}