CVE-2015-5334
📋 TL;DR
This is a critical stack-based buffer overflow vulnerability in LibreSSL's OBJ_obj2txt function caused by an off-by-one error. Attackers can exploit it via specially crafted X.509 certificates to crash applications or potentially execute arbitrary code. Systems using vulnerable versions of LibreSSL for SSL/TLS operations are affected.
💻 Affected Systems
- LibreSSL
📦 What is this software?
Libressl by Openbsd
Opensuse by Opensuse
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or persistent backdoor installation.
Likely Case
Denial of service through application crashes, disrupting SSL/TLS services and availability.
If Mitigated
Limited impact with proper network segmentation, certificate validation, and intrusion detection.
🎯 Exploit Status
Exploitation requires crafting malicious X.509 certificates. Public proof-of-concept code demonstrates crash/DoS; RCE would require additional exploitation techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: LibreSSL 2.3.1 and later
Vendor Advisory: http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.3.1-relnotes.txt
Restart Required: Yes
Instructions:
1. Update LibreSSL to version 2.3.1 or later using your system's package manager. 2. For OpenBSD: Use 'sysupgrade' or install from source. 3. For Linux distributions: Check vendor repositories for updated packages. 4. Rebuild and restart any applications statically linked to LibreSSL.
🔧 Temporary Workarounds
Certificate Validation Restriction
allImplement strict certificate validation to reject malformed or untrusted certificates.
# Configure applications to validate certificate chains strictly
# Use certificate pinning where possible
Network Segmentation
linuxIsolate systems using vulnerable LibreSSL versions from untrusted networks.
# Use firewall rules to restrict incoming SSL/TLS connections
iptables -A INPUT -p tcp --dport 443 -s trusted_networks -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Deploy network-based intrusion detection/prevention systems to block malicious certificates
- Implement application-level controls to sanitize or reject suspicious certificate inputs
🔍 How to Verify
Check if Vulnerable:
Check LibreSSL version: 'libressl version' or examine linked libraries in applications.Check Version:
libressl versionVerify Fix Applied:
Confirm version is 2.3.1 or later: 'libressl version' should show 2.3.1+.📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults in SSL/TLS functions
- Unexpected certificate parsing errors
- Failed SSL handshakes with malformed certificate alerts
Network Indicators:
- Unusual certificate structures in SSL/TLS traffic
- Multiple failed handshakes from single sources
SIEM Query:
source="*ssl*" AND (error="segmentation fault" OR error="buffer overflow" OR cert_parsing_failure)🔗 References
- http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.3.1-relnotes.txt
- http://lists.opensuse.org/opensuse-updates/2015-10/msg00050.html
- http://packetstormsecurity.com/files/133998/Qualys-Security-Advisory-LibreSSL-Leak-Overflow.html
- http://seclists.org/fulldisclosure/2015/Oct/75
- http://www.securityfocus.com/archive/1/archive/1/536692/100/0/threaded
- http://ftp.openbsd.org/pub/OpenBSD/LibreSSL/libressl-2.3.1-relnotes.txt
- http://lists.opensuse.org/opensuse-updates/2015-10/msg00050.html
- http://packetstormsecurity.com/files/133998/Qualys-Security-Advisory-LibreSSL-Leak-Overflow.html
- http://seclists.org/fulldisclosure/2015/Oct/75
- http://www.securityfocus.com/archive/1/archive/1/536692/100/0/threaded
