CVE-2025-11936
📋 TL;DR
A denial-of-service vulnerability in wolfSSL v5.8.2 allows remote attackers to crash TLS 1.3 connections by sending malicious ClientHello messages with duplicate KeyShareEntry values. This affects any system using the vulnerable wolfSSL library for TLS 1.3 connections. The attack requires no authentication and can be performed over the network.
💻 Affected Systems
- wolfSSL
📦 What is this software?
Wolfssl by Wolfssl
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption for TLS 1.3 connections, potentially causing application downtime and resource exhaustion on affected servers.
Likely Case
Temporary denial-of-service for TLS 1.3 connections, increased CPU/memory usage, and potential connection failures.
If Mitigated
Minimal impact with proper network controls and monitoring in place.
🎯 Exploit Status
Attack requires sending crafted TLS ClientHello messages. No authentication needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v5.8.3 or later
Vendor Advisory: https://github.com/wolfSSL/wolfssl/pull/9117
Restart Required: Yes
Instructions:
1. Update wolfSSL to version 5.8.3 or later
2. Recompile applications using wolfSSL
3. Restart affected services
🔧 Temporary Workarounds
Disable TLS 1.3
allTemporarily disable TLS 1.3 support to prevent exploitation
wolfSSL_CTX_SetMinVersion(ctx, WOLFSSL_TLSV1_2);
Rate limit TLS connections
allImplement connection rate limiting to reduce DoS impact
🧯 If You Can't Patch
- Implement network-level filtering to block malicious TLS packets
- Use load balancers with TLS termination to protect backend servers
🔍 How to Verify
Check if Vulnerable:
Check wolfSSL version with wolfSSL_lib_version() or equivalent functionCheck Version:
wolfSSL_lib_version()Verify Fix Applied:
Verify version is 5.8.3 or later and test TLS 1.3 connections📡 Detection & Monitoring
Log Indicators:
- Multiple failed TLS handshakes
- High CPU/memory usage during TLS processing
- Connection resets during ClientHello
Network Indicators:
- Unusual TLS ClientHello patterns
- Duplicate KeyShareEntry values in TLS traffic
SIEM Query:
source="tls_logs" AND (event="handshake_failure" OR event="connection_reset") AND protocol="TLSv1.3"