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How the CVE Works:
This vulnerability exploits the HTTP/2 protocol’s stream cancellation feature. An attacker can open numerous HTTP/2 streams and immediately send a RST_STREAM frame to cancel them, over and over in rapid succession. Each cancellation forces the server to perform cleanup work. Because the cost of processing these rapid resets is low for the client but high for the server, an attacker can create a massive, efficient Denial-of-Service (DoS) attack with relatively minimal resources. This request cancellation flood overwhelms the server’s capacity, leading to resource exhaustion and making the service unavailable to legitimate users. The attack is highly effective because it bypasses traditional rate-limiting and volumetric attack defenses, targeting the application layer directly.
Platform: NGINX and others
Version: Prior to 1.25.3
Vulnerability: HTTP/2 Rapid Reset
Severity: Critical
Date: October 2023
Prediction: Patched Q4 2023
What Undercode Say:
Check for HTTP/2 support
curl -I –http2 https://target.com | grep -i “HTTP/”
Test with h2load (observe stream errors)
h2load -n 100000 -c 100 -m 100 https://target.com
Sample detection log pattern
grep “RST_STREAM” /var/log/nginx/access.log | wc -l
How Exploit:
Attacker scripts send continuous HTTP/2 requests followed by immediate RST_STREAM frames, creating a high-throughput cancellation loop that consumes server resources with minimal client-side cost.
Protection from this CVE:
Apply vendor patches. Disable HTTP/2 if not required. Implement upstream rate-limiting per connection. Use WAF rules targeting abnormal RST_STREAM frequency.
Impact:
High-throughput Denial-of-Service leading to complete service unavailability. Exploitation is simple with public PoC scripts. Affects any server using vulnerable HTTP/2 implementations.
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Sources:
Reported By: github.com
Extra Source Hub:
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