CVE-2023-26464: Apache Log4j DOS Vulnerability

CVE-2023-26464 Overview

CVE-2023-26464 is a high-severity Insecure Deserialization vulnerability affecting Apache Log4j 1.x when used with the Chainsaw or SocketAppender components on JRE versions less than 1.7. An attacker who can cause a logging entry involving a specially-crafted, deeply nested hashmap or hashtable to be processed could exhaust available memory in the virtual machine, resulting in a Denial of Service condition when the malicious object is deserialized.

This vulnerability is particularly significant because it affects a legacy, unsupported version of Log4j. The Apache Software Foundation has marked this vulnerability as "UNSUPPORTED WHEN ASSIGNED," meaning the affected Log4j 1.x branch is no longer receiving security updates.

Critical Impact

Memory exhaustion Denial of Service affecting applications using unsupported Log4j 1.x with Chainsaw or SocketAppender on older JRE versions (< 1.7). No patches available for Log4j 1.x - migration to Log4j 2.x is required.

Affected Products

• Apache Log4j versions before 2.x
• Applications using Chainsaw component with Log4j 1.x
• Applications using SocketAppender component with Log4j 1.x on JRE < 1.7

Discovery Timeline

• 2023-03-10 - CVE-2023-26464 published to NVD
• 2025-02-13 - Last updated in NVD database

Technical Details for CVE-2023-26464

Vulnerability Analysis

This vulnerability (CWE-502: Deserialization of Untrusted Data) exploits the way Log4j 1.x processes serialized Java objects through the Chainsaw and SocketAppender components. When an attacker crafts a deeply nested hashmap or hashtable structure and causes it to be logged, the deserialization process attempts to reconstruct the entire object graph in memory.

The fundamental issue lies in how Java's native deserialization handles complex nested data structures. Each level of nesting in the malicious payload exponentially increases memory consumption during object reconstruction. On JRE versions prior to 1.7, certain memory management optimizations that could mitigate this attack are not present, making these environments particularly susceptible.

The Chainsaw component, a GUI-based log viewer, and SocketAppender, which sends logging events over network sockets, both accept serialized objects as part of their normal operation. This creates an attack surface where malicious serialized data can be injected into the logging pipeline.

Root Cause

The root cause is the unrestricted deserialization of Java objects in the Chainsaw and SocketAppender components without proper validation of object depth or complexity. Log4j 1.x does not implement safeguards to limit the resource consumption during deserialization of nested collection objects like HashMap or Hashtable, allowing attackers to craft payloads that consume exponential memory resources.

Attack Vector

The attack vector is network-based, requiring no privileges or user interaction. An attacker must be able to inject a specially-crafted serialized Java object into a logging entry that gets processed by either the Chainsaw or SocketAppender component. This could be achieved by:

1. Sending malicious serialized data to an exposed SocketAppender endpoint
2. Causing an application to log attacker-controlled data that includes the malicious nested structure
3. Exploiting logging configurations that process untrusted input through these components

The deeply nested hashmap or hashtable structure triggers recursive memory allocation during deserialization, eventually exhausting the JVM heap space and causing an OutOfMemoryError, resulting in application crash or unresponsiveness.

Detection Methods for CVE-2023-26464

Indicators of Compromise

• Sudden spikes in JVM heap memory usage correlated with logging activity
• OutOfMemoryError exceptions in application logs referencing deserialization operations
• Unusual network traffic patterns to SocketAppender listening ports
• Application crashes or hangs during log processing operations

Detection Strategies

• Monitor JVM memory metrics for anomalous consumption patterns during logging operations
• Implement application-level logging to detect deserialization exceptions or errors
• Scan application dependencies to identify Log4j 1.x usage with Chainsaw or SocketAppender configurations
• Review logging configurations for exposed SocketAppender endpoints accepting remote connections

Monitoring Recommendations

• Enable Java garbage collection logging to detect memory pressure events
• Configure alerting on JVM heap utilization thresholds (e.g., > 80% sustained usage)
• Monitor application availability and response times for degradation patterns
• Audit network access to any SocketAppender listener ports

How to Mitigate CVE-2023-26464

Immediate Actions Required

• Migrate from Log4j 1.x to Log4j 2.x as the primary remediation strategy
• Disable or remove Chainsaw and SocketAppender components if migration is not immediately possible
• Restrict network access to any SocketAppender listening endpoints
• Upgrade JRE to version 1.7 or later to benefit from improved memory handling

Patch Information

No patch is available for Log4j 1.x as it has reached end-of-life and is no longer supported by the Apache Software Foundation. The official recommendation is to upgrade to Log4j 2.x, which addresses this vulnerability and includes numerous security improvements. For additional context, refer to the Apache Mailing List Discussion and the NetApp Security Advisory.

Workarounds

• Remove Chainsaw and SocketAppender from Log4j configurations to eliminate the attack surface
• Implement network segmentation to prevent untrusted access to logging endpoints
• Configure JVM memory limits to contain the impact of memory exhaustion attacks
• Deploy application-level input validation to filter potentially malicious serialized objects before logging

# Configuration example - Disable SocketAppender in log4j.properties
# Remove or comment out SocketAppender configuration
# log4j.appender.socket=org.apache.log4j.net.SocketAppender
# log4j.appender.socket.RemoteHost=localhost
# log4j.appender.socket.Port=4445

# Alternative: Use FileAppender instead
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=/var/log/application.log
log4j.appender.file.MaxFileSize=10MB
log4j.appender.file.MaxBackupIndex=10
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n