CVE-2019-17571 in Communications Unified Assurance
Summary
by MITRE
Included in Log4j 1.2 is a SocketServer class that is vulnerable to deserialization of untrusted data which can be exploited to remotely execute arbitrary code when combined with a deserialization gadget when listening to untrusted network traffic for log data. This affects Log4j versions up to 1.2 up to 1.2.17.
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Analysis
by VulDB Data Team • 05/29/2026
The vulnerability identified as CVE-2019-17571 represents a critical deserialization flaw within Apache Log4j version 1.2 series, specifically affecting versions up to 1.2.17. This vulnerability resides within the SocketServer class component of the logging framework, which serves as a network listener for log data transmission. The flaw enables remote code execution when the vulnerable Log4j component processes untrusted network traffic containing malicious serialized objects. The vulnerability operates through the exploitation of Java deserialization mechanisms, where the SocketServer accepts serialized data from network connections and attempts to deserialize it without proper validation of the source or content. This design flaw creates a pathway for attackers to inject malicious code that executes within the context of the Log4j application process, potentially leading to complete system compromise.
The technical exploitation of this vulnerability follows a well-documented pattern that aligns with CWE-502, which describes deserialization of untrusted data as a critical security weakness. Attackers can leverage this vulnerability by crafting malicious serialized objects that contain malicious payloads designed to execute arbitrary code when deserialized by the vulnerable SocketServer component. The attack typically involves sending specially crafted log data over the network to a Log4j instance configured to listen for incoming connections through the SocketServer. When the system processes this data, the deserialization process triggers the execution of the attacker-controlled code, potentially allowing for remote command execution, privilege escalation, or data exfiltration. The vulnerability's impact is amplified because Log4j is widely deployed across enterprise environments and is often used as a foundational logging component in many applications and systems.
The operational impact of CVE-2019-17571 extends beyond individual system compromise to threaten entire network infrastructures due to Log4j's widespread adoption across various platforms and applications. Organizations using vulnerable versions of Log4j 1.2 face significant risk of unauthorized access, data breaches, and system infiltration when their logging components are exposed to untrusted network traffic. The vulnerability's remote exploitation capability means that attackers can target systems without requiring local access or credentials, making it particularly dangerous in environments where logging services are exposed to external networks. Security teams must consider that many applications may be vulnerable even if they don't directly use Log4j's SocketServer functionality, as the framework is often embedded within larger applications and frameworks. The attack surface is further expanded when considering that Log4j's SocketServer can be configured to accept connections from multiple network interfaces, potentially exposing systems to attacks from various network locations.
Mitigation strategies for CVE-2019-17571 require immediate action to address the root cause of the vulnerability. The most effective approach involves upgrading to a patched version of Log4j, specifically versions 1.2.18 or later, which contain fixes for the deserialization vulnerability. Organizations should implement network segmentation to restrict access to Log4j SocketServer components, ensuring that only trusted sources can connect to logging services. Network firewalls and access control lists should be configured to block external connections to logging ports and services. Additionally, implementing input validation and sanitization measures can help prevent malicious serialized objects from being processed by vulnerable systems. Security monitoring should be enhanced to detect unusual network traffic patterns or attempts to exploit the vulnerability. The remediation process should include thorough inventory assessment to identify all systems running vulnerable Log4j versions and comprehensive testing of patched environments to ensure compatibility and proper functionality. Organizations should also consider implementing application-level controls and runtime protection mechanisms to detect and prevent deserialization attacks, aligning with ATT&CK techniques related to deserialization attacks and remote code execution.