🪲 Bug Bounty Pro Tip: #H2C Upgrade Bypass
Target: Applications using HTTP/2 Cleartext (h2c) upgrades.
The Core Idea: Many Web Application Firewalls (WAFs) and reverse proxies process HTTP/1.1 but fail to correctly inspect traffic after it's upgraded to HTTP/2.
How to Test:
1. Find a target that accepts an Upgrade: h2c header (common in Java, gRPC, and some reverse proxies like Nginx).
2. Send an initial HTTP/1.1 request with the upgrade header:
3. If the server agrees (responds with HTTP/1.1 101 Switching Protocols), the connection is now HTTP/2.
4. The Bypass: Craft and send malformed or smuggled HTTP/2 frames (e.g., with the :method header set to GET or POST). The downstream WAF may not parse this, allowing you to access internal endpoints or bypass security controls.
Why it works: The security boundary often only exists at the HTTP/1.1 layer. Once upgraded, your HTTP/2 traffic might be forwarded directly to the backend without inspection.
#BugBounty #Hacking #WebSecurity #WAFBypass #HTTP2
Target: Applications using HTTP/2 Cleartext (h2c) upgrades.
The Core Idea: Many Web Application Firewalls (WAFs) and reverse proxies process HTTP/1.1 but fail to correctly inspect traffic after it's upgraded to HTTP/2.
How to Test:
1. Find a target that accepts an Upgrade: h2c header (common in Java, gRPC, and some reverse proxies like Nginx).
2. Send an initial HTTP/1.1 request with the upgrade header:
GET / HTTP/1.1
Host: example.com
Upgrade: h2c
Connection: Upgrade
3. If the server agrees (responds with HTTP/1.1 101 Switching Protocols), the connection is now HTTP/2.
4. The Bypass: Craft and send malformed or smuggled HTTP/2 frames (e.g., with the :method header set to GET or POST). The downstream WAF may not parse this, allowing you to access internal endpoints or bypass security controls.
Why it works: The security boundary often only exists at the HTTP/1.1 layer. Once upgraded, your HTTP/2 traffic might be forwarded directly to the backend without inspection.
#BugBounty #Hacking #WebSecurity #WAFBypass #HTTP2
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