CVE-2015-5333
📋 TL;DR
A memory leak vulnerability in LibreSSL's OBJ_obj2txt function allows remote attackers to cause denial of service by consuming all available memory. Attackers can trigger this by sending X.509 certificates containing numerous ASN.1 object identifiers. Systems using vulnerable LibreSSL versions for TLS/SSL operations are affected.
💻 Affected Systems
- LibreSSL
📦 What is this software?
Libressl by Openbsd
Opensuse by Opensuse
⚠️ Risk & Real-World Impact
Worst Case
Complete system unavailability due to memory exhaustion, potentially crashing services or the entire system, leading to extended downtime.
Likely Case
Service degradation or temporary unavailability of affected services using LibreSSL for certificate validation, requiring restart to recover memory.
If Mitigated
Minimal impact with proper monitoring and memory limits, though some service disruption may still occur during attack.
🎯 Exploit Status
Exploitation requires sending specially crafted X.509 certificates to vulnerable services. Public proof-of-concept code exists in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 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 Linux: Use 'apt-get update && apt-get upgrade libressl' (Debian/Ubuntu) or 'yum update libressl' (RHEL/CentOS). 3. Restart all services using LibreSSL. 4. Recompile any applications statically linked to LibreSSL.
🔧 Temporary Workarounds
Rate limit certificate processing
allImplement rate limiting on services accepting certificates to reduce attack surface
# Configure rate limiting in your web server or application firewall
Memory usage monitoring
allMonitor memory consumption of services using LibreSSL and implement automatic restarts
# Set up monitoring with tools like Nagios, Zabbix, or custom scripts
🧯 If You Can't Patch
- Implement strict certificate validation and reject certificates with excessive ASN.1 object identifiers
- Deploy network-based protections like WAFs or IPS to detect and block malicious certificate traffic
🔍 How to Verify
Check if Vulnerable:
Check LibreSSL version: 'libressl version' or 'openssl version' if LibreSSL is installed as openssl replacementCheck Version:
libressl versionVerify Fix Applied:
Verify version is 2.3.1 or higher: 'libressl version | grep -q "2.3.1\|^2\.[4-9]\|^3\." && echo "Patched"'📡 Detection & Monitoring
Log Indicators:
- Unusual memory consumption spikes in system logs
- Service crashes or restarts related to certificate processing
- Error logs mentioning certificate parsing failures
Network Indicators:
- High volume of certificate exchanges to single endpoints
- Unusually large certificate payloads in network traffic
SIEM Query:
source="*ssl*" OR source="*certificate*" AND (memory_usage>90% OR process_crash=true)🔗 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://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://www.securityfocus.com/archive/1/archive/1/536692/100/0/threaded
