mitmproxy binaries embed a vulnerable python-hyper/h2 dependency
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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | mitmproxy | < 12.1.2 | 12.1.2 |
References
- CVSS vector
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- Weakness (CWE)
CWE-1395, CWE-444- Platform
- Python (PyPI)
- Package
mitmproxy- Disclosed
- 25.08.2025
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - GHSA-63cx-g855-hvv4 - CC BY 4.0
Vulnerability history: mitmproxy
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 6
- First → latest
- 07.2018 04.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 3
- High 1
- Medium 2
Disclosures per year
- 2018: 1
- 2019: 0
- 2020: 0
- 2021: 1
- 2022: 1
- 2023: 0
- 2024: 0
- 2025: 2
- 2026: 1
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mitmproxy binaries embed a vulnerable python-hyper/h2 dependency this entry
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