CVE-2025-54939: LiteSpeed QUIC Library Memory Leak Flaw

CVE-2025-54939 Overview

CVE-2025-54939 is a memory leak vulnerability in the LiteSpeed QUIC (LSQUIC) Library before version 4.3.1. The vulnerability exists in the lsquic_engine_packet_in() function, which fails to properly deallocate memory during packet processing. This flaw can be exploited remotely by unauthenticated attackers to cause resource exhaustion and denial of service conditions on affected servers.

The LSQUIC library is a widely-deployed implementation of the QUIC protocol used by LiteSpeed Web Server, LiteSpeed Web ADC, and OpenLiteSpeed. Due to the network-accessible nature of this vulnerability and the lack of authentication requirements, servers running vulnerable versions are at significant risk of availability disruption.

Critical Impact

Remote attackers can exhaust server memory resources through the lsquic_engine_packet_in() memory leak, causing denial of service on LiteSpeed-powered web infrastructure without authentication.

Affected Products

• LiteSpeed Web ADC (versions prior to patched releases)
• LiteSpeed Web Server (versions prior to patched releases)
• LSQUIC Library (versions before 4.3.1)
• OpenLiteSpeed (versions prior to patched releases)

Discovery Timeline

• 2025-07-17 - LSQUIC version 4.3.1 released with fix for memory leak
• 2025-08-01 - CVE-2025-54939 published to NVD
• 2025-08-18 - LiteSpeed Technologies releases security update advisory
• 2025-08-27 - Last updated in NVD database

Technical Details for CVE-2025-54939

Vulnerability Analysis

The vulnerability stems from improper memory management in the LSQUIC library's packet processing engine. When the lsquic_engine_packet_in() function processes incoming QUIC packets, it allocates memory resources that are not properly freed under certain conditions. This memory leak can be triggered during the pre-handshake phase of QUIC connections, meaning attackers do not need to complete the connection establishment process to exploit the flaw.

The denial of service impact is particularly severe because QUIC operates over UDP, allowing attackers to send malicious packets with spoofed source addresses. Combined with the low attack complexity and no required privileges, this creates favorable conditions for amplification-style attacks against target infrastructure.

Root Cause

The root cause is classified under CWE-770 (Allocation of Resources Without Limits or Throttling) and CWE-401 (Missing Release of Memory after Effective Lifetime). The lsquic_engine_packet_in() function allocates memory for packet processing but fails to release this memory in specific code paths, leading to progressive memory exhaustion as malicious packets are processed.

Attack Vector

The attack vector is network-based and requires no user interaction or authentication. An attacker can send specially crafted QUIC packets to a vulnerable server, triggering the memory leak in lsquic_engine_packet_in(). Since the vulnerability is exploitable during the pre-handshake phase, attackers can repeatedly send malicious packets to rapidly deplete available server memory, ultimately causing the service to crash or become unresponsive.

The following patch was applied in version 4.3.1 to address the vulnerability:

+2025-07-17
+    - 4.3.1
+    - Fix a memory leak in lsquic_engine_packet_in()
+
 2025-06-17
     - 4.3.0
     - Add WebTransport support.

Source: GitHub lsquic Commit

Detection Methods for CVE-2025-54939

Indicators of Compromise

• Abnormal memory consumption growth on LiteSpeed server processes
• Elevated UDP traffic on QUIC ports (typically port 443)
• Server processes crashing or becoming unresponsive due to out-of-memory conditions
• Unusual volume of incomplete QUIC handshake attempts in server logs

Detection Strategies

• Monitor memory utilization trends on servers running LSQUIC-based applications
• Implement network-level monitoring for anomalous QUIC packet volumes
• Configure alerting for rapid memory consumption increases in LiteSpeed processes
• Review system logs for OOM (Out of Memory) killer activity targeting web server processes

Monitoring Recommendations

• Deploy application performance monitoring (APM) to track memory allocation patterns in LSQUIC components
• Establish baseline metrics for normal QUIC traffic volumes and alert on deviations
• Enable detailed logging for QUIC connection attempts to identify potential attack patterns
• Implement rate limiting on UDP traffic at the network perimeter to mitigate volumetric attacks

How to Mitigate CVE-2025-54939

Immediate Actions Required

• Upgrade LSQUIC library to version 4.3.1 or later immediately
• Update LiteSpeed Web Server, LiteSpeed Web ADC, and OpenLiteSpeed to patched versions
• Review the LiteSpeed Security Update for specific patched version numbers
• Implement rate limiting for incoming QUIC connections as a temporary protective measure

Patch Information

LiteSpeed Technologies has released version 4.3.1 of the LSQUIC library to address this vulnerability. The fix corrects the memory leak in lsquic_engine_packet_in(). The patch is available through the official GitHub repository and through LiteSpeed's product update channels. Organizations should consult the LiteSpeed Security Update for comprehensive guidance on applying the patch to their specific deployment.

Workarounds

• Configure firewall rules to limit UDP traffic on QUIC ports from untrusted sources
• Implement connection rate limiting at load balancers or reverse proxies
• If QUIC is not required, disable HTTP/3 and QUIC support to eliminate the attack surface
• Deploy DDoS protection services capable of identifying and filtering malicious QUIC traffic

# Example: Rate limit UDP connections on QUIC port using iptables
iptables -A INPUT -p udp --dport 443 -m limit --limit 100/sec --limit-burst 200 -j ACCEPT
iptables -A INPUT -p udp --dport 443 -j DROP