GHSA-63cx-g855-hvv4
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- None
What each source reports
GitHub Advisories Score used
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.
- Record
GHSA-63cx-g855-hvv4- CVSS 4.0
- 6.9 Medium
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-444, CWE-1395
- Updated
- 2026-11-02
OSV
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.
- Record
GHSA-63cx-g855-hvv4- CVSS 4.0
- 6.9 Medium
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-1395, CWE-444
- Updated
- 2026-11-02
Affected packages
| Package | Affected | Fixed |
|---|---|---|
mitmproxyPyPI | through 12.1.1 | 12.1.2 |
mitmproxyPyPI | before 12.1.2, plus listed versions 0.100.10.10.110.11.10.11.2 Show 45 moreShow less0.11.30.12.00.12.10.130.14.00.150.160.170.18.10.18.20.18.30.80.8.10.90.9.10.9.21.0.01.0.11.0.210.0.010.1.010.1.110.1.210.1.310.1.410.1.510.1.610.2.010.2.110.2.210.2.310.2.410.3.010.3.110.4.010.4.110.4.211.0.011.0.111.0.211.1.011.1.211.1.312.0.012.0.1 | 12.1.2 |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | GitHub Advisories, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
GHSA-63cx-g855-hvv4 is a medium vulnerability (CVSS 6.9) in mitmproxy, published August 25, 2025. No source lists public exploit code. Fixed in mitmproxy 12.1.2.
References
Left out here: 33 versions. The JSON record has them.