CVE-2023-6378: Qos Logback DOS Vulnerability

CVE-2023-6378 Overview

A serialization vulnerability exists in the logback receiver component of logback version 1.4.11 that allows an attacker to mount a Denial-of-Service (DoS) attack by sending poisoned data. Logback is a widely-used logging framework for Java applications, serving as a successor to the popular log4j project. This vulnerability specifically targets the receiver component, which is responsible for accepting log events from remote sources over the network.

Critical Impact

Attackers can remotely trigger a Denial-of-Service condition by sending specially crafted serialized data to the logback receiver, potentially disrupting critical application logging infrastructure and dependent services.

Affected Products

• QOS Logback version 1.4.11
• QOS Logback versions prior to 1.3.12 (1.3.x branch)
• QOS Logback versions prior to 1.4.12 (1.4.x branch)

Discovery Timeline

• 2023-11-29 - CVE CVE-2023-6378 published to NVD
• 2024-11-29 - Last updated in NVD database

Technical Details for CVE-2023-6378

Vulnerability Analysis

This vulnerability is classified as CWE-502: Deserialization of Untrusted Data. The logback receiver component accepts serialized Java objects over the network without adequate validation, enabling attackers to submit malicious payloads that trigger resource exhaustion or application crashes during the deserialization process.

The attack can be conducted remotely over the network without requiring any prior authentication or user interaction. While the vulnerability does not compromise data confidentiality or integrity, it poses a significant availability risk to systems running vulnerable logback configurations with the receiver component enabled.

Root Cause

The root cause lies in the insecure deserialization practices within the logback receiver component. When the receiver processes incoming log events, it deserializes Java objects without properly validating or sanitizing the incoming data stream. This allows attackers to craft malicious serialized objects that, when processed, consume excessive resources or trigger exception conditions that result in service disruption.

The receiver component in logback is designed to accept log events from remote SocketAppender instances, making it inherently exposed to network-based attacks when enabled. The lack of input validation on the serialization stream creates an attack surface that can be exploited without authentication.

Attack Vector

The attack vector for this vulnerability is network-based. An attacker can exploit this vulnerability by:

1. Identifying a target system running logback with the receiver component enabled
2. Crafting a malicious serialized payload designed to trigger a DoS condition
3. Sending the poisoned data to the logback receiver endpoint
4. Causing the target application's logging infrastructure to become unavailable

The vulnerability does not require attacker authentication, specialized access, or user interaction, making it straightforward to exploit against exposed receiver endpoints.

Detection Methods for CVE-2023-6378

Indicators of Compromise

• Unusual network traffic patterns to logback receiver ports (typically TCP connections)
• Application crashes or hangs related to logback receiver threads
• Increased memory consumption or CPU utilization in Java applications using logback
• Exception logs indicating deserialization failures or ObjectInputStream errors

Detection Strategies

• Monitor network connections to logback receiver endpoints for anomalous traffic volumes or connection patterns
• Implement application performance monitoring to detect sudden resource exhaustion in logging components
• Review application logs for serialization-related exceptions or stack traces involving ch.qos.logback.classic.net.server packages
• Deploy network intrusion detection rules targeting malformed Java serialization streams

Monitoring Recommendations

• Enable verbose logging for logback receiver components during investigation periods
• Set up alerts for application restarts or crashes in services using logback receivers
• Monitor JVM heap and thread metrics for applications with receiver functionality enabled
• Implement network flow analysis to baseline normal receiver traffic and detect deviations

How to Mitigate CVE-2023-6378

Immediate Actions Required

• Upgrade logback to version 1.3.12 or later for the 1.3.x branch
• Upgrade logback to version 1.4.12 or later for the 1.4.x branch
• If upgrading is not immediately possible, disable the logback receiver component until patches can be applied
• Review network exposure of logback receiver endpoints and implement firewall rules to restrict access

Patch Information

QOS has released patched versions addressing this vulnerability. Users should upgrade to:

• Logback 1.3.12 or later for applications on the 1.3.x branch
• Logback 1.4.12 or later for applications on the 1.4.x branch

For detailed release information, refer to the Logback Release Notes 1.3.12. Additional vendor guidance is available in the NetApp Security Advisory NTAP-20241129-0012.

Workarounds

• Disable the logback receiver component if it is not required for your application's functionality
• Implement network segmentation to isolate logback receiver endpoints from untrusted networks
• Use firewall rules to restrict access to logback receiver ports to known, trusted log sources only
• Consider switching to alternative log aggregation mechanisms that do not rely on Java serialization

# Configuration example - Disable receiver in logback.xml
# Remove or comment out the receiver configuration:
# <receiver class="ch.qos.logback.classic.net.server.ServerSocketReceiver">
#   <port>4560</port>
# </receiver>

# Alternatively, restrict network access via firewall
iptables -A INPUT -p tcp --dport 4560 -s trusted_source_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 4560 -j DROP