GHSA-63cx-g855-hvv4 — mitmproxy
GHSA-63cx-g855-hvv4 is a security vulnerability in mitmproxy. A fix is available for mitmproxy — see the affected versions and patch details below.
mitmproxy binaries embed a vulnerable python-hyper/h2 dependency
Real-World Exposure
mitmproxyReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | mitmproxy | all versions | 12.1.2pip install --upgrade 'mitmproxy==12.1.2' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mitmproxy, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update mitmproxy to 12.1.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-63cx-g855-hvv4 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-63cx-g855-hvv4 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-63cx-g855-hvv4. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-63cx-g855-hvv4 in your dependencies?
O3 Security finds GHSA-63cx-g855-hvv4 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.