CVE-2025-54939
📋 TL;DR
CVE-2025-54939 is a memory leak vulnerability in LiteSpeed's LSQUIC library that occurs when processing QUIC packets before handshake completion. This allows remote attackers to cause denial of service through resource exhaustion. Systems using LSQUIC versions before 4.3.1 for QUIC/HTTP3 implementations are affected.
💻 Affected Systems
- LiteSpeed Web Server
- OpenLiteSpeed
- Applications using LSQUIC library
📦 What is this software?
Litespeed Web Adc by Litespeedtech
Litespeed Web Server by Litespeedtech
Lsquic by Litespeedtech
Openlitespeed by Litespeedtech
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attackers can send crafted QUIC packets to exhaust server memory, leading to complete service disruption and potential system instability.
Likely Case
Targeted DoS attacks against vulnerable servers causing performance degradation and intermittent service interruptions.
If Mitigated
With proper rate limiting and memory monitoring, impact is limited to temporary performance issues.
🎯 Exploit Status
Exploitation requires sending QUIC packets before handshake completion
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: LSQUIC 4.3.1 or later
Vendor Advisory: https://blog.litespeedtech.com/2025/08/18/litespeed-security-update/
Restart Required: Yes
Instructions:
1. Update LSQUIC library to version 4.3.1 or later
2. Recompile applications using LSQUIC
3. Restart affected services
4. For LiteSpeed Web Server: Update to latest version that includes LSQUIC 4.3.1
🔧 Temporary Workarounds
Disable QUIC/HTTP3
allTemporarily disable QUIC protocol support to prevent exploitation
# In LiteSpeed Web Server: Disable QUIC in server configuration
# In applications: Disable LSQUIC initialization or use alternative HTTP implementations
Rate Limit QUIC Packets
linuxImplement network-level rate limiting for QUIC traffic
# Example iptables rule for QUIC (UDP port 443)
iptables -A INPUT -p udp --dport 443 -m limit --limit 1000/minute -j ACCEPT
iptables -A INPUT -p udp --dport 443 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to limit QUIC traffic to trusted sources only
- Deploy memory monitoring and alerting for abnormal memory consumption patterns
🔍 How to Verify
Check if Vulnerable:
Check LSQUIC library version or application version that includes LSQUICCheck Version:
ldd --version | grep lsquic OR check application documentation for version infoVerify Fix Applied:
Verify LSQUIC version is 4.3.1 or later and monitor memory usage during QUIC traffic📡 Detection & Monitoring
Log Indicators:
- Abnormal memory consumption patterns
- QUIC connection failures before handshake
- System out-of-memory errors
Network Indicators:
- High volume of QUIC packets from single sources
- QUIC packets without follow-up handshake attempts
SIEM Query:
source="*" ("out of memory" OR "OOM" OR "memory exhausted") AND ("QUIC" OR "lsquic" OR "HTTP/3")🔗 References
- https://blog.litespeedtech.com/2025/08/18/litespeed-security-update/
- https://github.com/litespeedtech/lsquic/blob/70486141724f85e97b08f510673e29f399bbae8f/CHANGELOG#L1-L3
- https://github.com/litespeedtech/lsquic/commit/4cd9252e77fb4a36b572e2167a84067d603d3b23
- https://www.imperva.com/blog/quic-leak-cve-2025-54939-new-high-risk-pre-handshake-remote-denial-of-service-in-lsquic-quic-implementation/
