CVE-2025-4820
📋 TL;DR
This vulnerability in Cloudflare's quiche QUIC library allows attackers to manipulate congestion control, causing affected systems to send data faster than network paths can handle. This affects any system using vulnerable versions of quiche for QUIC/HTTP3 communication, potentially leading to network congestion and performance degradation.
💻 Affected Systems
- Cloudflare quiche
📦 What is this software?
Quiche by Cloudflare
⚠️ Risk & Real-World Impact
Worst Case
Network congestion causing packet loss, degraded performance for all users on affected paths, and potential denial of service conditions on constrained networks.
Likely Case
Temporary performance degradation and increased packet loss on affected connections, with potential impact on application responsiveness.
If Mitigated
Minimal impact with proper network monitoring and rate limiting in place.
🎯 Exploit Status
Requires establishing QUIC handshake and manipulating ACK frames as described in RFC 9000 Section 21.4.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.24.4
Vendor Advisory: https://github.com/cloudflare/quiche/security/advisories/GHSA-2v9p-3p3h-w56j
Restart Required: Yes
Instructions:
1. Update quiche dependency to version 0.24.4 or later. 2. Rebuild and redeploy applications using quiche. 3. Restart affected services.
🔧 Temporary Workarounds
Disable QUIC/HTTP3
allTemporarily disable QUIC/HTTP3 protocols to prevent exploitation
Configure applications to use HTTP/1.1 or HTTP/2 instead of HTTP/3
Network Rate Limiting
allImplement network-level rate limiting for QUIC traffic
Configure firewall/load balancer to limit QUIC connection rates
🧯 If You Can't Patch
- Implement network monitoring for abnormal QUIC traffic patterns
- Deploy network devices that can detect and mitigate congestion control manipulation
🔍 How to Verify
Check if Vulnerable:
Check quiche version in your application dependencies or build configurationCheck Version:
Check your dependency manifest (Cargo.toml for Rust, package.json for Node.js, etc.) for quiche versionVerify Fix Applied:
Verify quiche version is 0.24.4 or later after update📡 Detection & Monitoring
Log Indicators:
- Unusual QUIC connection patterns
- Increased packet loss reports
- Congestion window size anomalies
Network Indicators:
- Abnormal QUIC ACK frame patterns
- Sudden increases in QUIC traffic rates
- Network congestion alerts
SIEM Query:
Search for QUIC protocol anomalies or sudden traffic spikes from single sources