Security tool · smuggling
h2csmuggler
Tests for HTTP/2 cleartext (h2c) smuggling to bypass reverse-proxy access controls and reach restricted internal endpoints.
Overview
Where h2csmuggler fits
Tests for HTTP/2 cleartext (h2c) smuggling to bypass reverse-proxy access controls and reach restricted internal endpoints.
Detection-first use
Start with the least intrusive template that can distinguish your hypothesis from a normal response. Preserve raw output and a negative control.
Install
Installation references
Install with gitAuthorization required
git clone https://github.com/BishopFox/h2csmuggler && cd h2csmuggler/python && pip install -r requirements.txt- Positive signal
- Tool-specific output that supports the stated hypothesis.
- Negative control
- No result, or identical behavior against a known-safe control.
- Intrusiveness
- Review flags and target scope before execution.
Test safely
Command templates
Attempt h2c upgradeAuthorization required
Populate placeholders only with assets that are explicitly in scope.
python3 h2csmuggler.py -x {url} {target}- Positive signal
- Tool-specific output that supports the stated hypothesis.
- Negative control
- No result, or identical behavior against a known-safe control.
- Intrusiveness
- Review flags and target scope before execution.
Related
Continue the workflow
Sources
Attribution and verification
Version history: normalized permanent page created 2026-08-20. Upstream activity and popularity are separate signals and do not establish tool safety.