Horizon Alert
Summary of the vulnerability and why it matters
A vulnerability in the HTTP/2 protocol can be used to overwhelm servers with requests, leading to denial-of-service attacks. This issue is significant because it can disrupt service availability for a wide range of internet-facing applications and infrastructure.
- Can cause widespread service outages.
- Affects systems processing web traffic.
- Exploited in the wild recently.
Attack Path
How an attacker could exploit the issue
An attacker can exploit this vulnerability by sending a large number of stream reset frames to a vulnerable HTTP/2 server. This exhausts server resources, leading to a denial of service. This attack requires no authentication or user interaction and can be launched remotely.
- Targets web servers and proxies.
- Exploits HTTP/2 stream reset mechanism.
- Causes server resource exhaustion.
Live Threat
Current exploitation, exposure, and threat context
This vulnerability allows for large-scale denial-of-service attacks by overwhelming servers with rapid request cancellations. Observed exploitation in August-October 2023 indicates immediate threat potential. Given the widespread use of HTTP/2 across web infrastructure, attackers are likely to continue leveraging this for disruptive attacks.
- Exploited in the wild.
- Public exploit and KEV listing exist.
- Recent exploitation signals ongoing threat.
Priority actions
Operational Fix
Recommended remediation, mitigation, and detection steps
Prioritize identifying and blocking the massive DDoS traffic associated with this vulnerability. Focus on systems that use HTTP/2, especially internet-facing web servers, load balancers, and reverse proxies. Implement rapid response for affected services, as this has been actively exploited.
- Block malicious HTTP/2 traffic.
- Update affected HTTP/2 implementations.
- Monitor for resource exhaustion.
