CVE-2020-2883: Oracle WebLogic Server RCE Vulnerability

CVE-2020-2883 Overview

CVE-2020-2883 is a critical insecure deserialization vulnerability affecting the Core component of Oracle WebLogic Server, a widely deployed Java EE application server within Oracle Fusion Middleware. This vulnerability allows an unauthenticated attacker with network access via IIOP (Internet Inter-ORB Protocol) or T3 protocol to execute arbitrary code and achieve complete takeover of the affected WebLogic Server instance.

The vulnerability is particularly dangerous because it requires no authentication, no user interaction, and is easily exploitable from the network. Successful exploitation grants attackers full control over the target server, enabling them to steal sensitive data, deploy malware, pivot to other systems on the network, or disrupt business operations entirely.

Critical Impact

This vulnerability is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, indicating active exploitation in the wild. Unauthenticated remote attackers can achieve complete server takeover with full confidentiality, integrity, and availability impact.

Affected Products

• Oracle WebLogic Server 10.3.6.0.0
• Oracle WebLogic Server 12.1.3.0.0
• Oracle WebLogic Server 12.2.1.3.0
• Oracle WebLogic Server 12.2.1.4.0

Discovery Timeline

• 2020-04-15 - CVE-2020-2883 published to NVD
• 2025-10-27 - Last updated in NVD database

Technical Details for CVE-2020-2883

Vulnerability Analysis

CVE-2020-2883 is an insecure deserialization vulnerability in Oracle WebLogic Server's Core component. The vulnerability exists in how WebLogic Server processes serialized Java objects received via the T3 and IIOP protocols. These protocols are used for communication between WebLogic Server instances and for remote method invocation (RMI).

When a malicious serialized object is sent to the T3 or IIOP listener ports (typically TCP port 7001 or 7002), the WebLogic Server deserializes the object without adequate validation. Attackers can craft malicious serialized payloads using known Java deserialization gadget chains that, when deserialized, trigger arbitrary code execution on the server.

The ease of exploitation is significant—the attack requires only network connectivity to the WebLogic Server's T3/IIOP ports with no authentication credentials. This makes internet-exposed WebLogic Servers particularly vulnerable to automated scanning and exploitation campaigns.

Root Cause

The root cause of CVE-2020-2883 lies in insufficient input validation and unsafe deserialization practices within WebLogic Server's handling of incoming serialized Java objects. The T3 and IIOP protocol handlers do not adequately filter or validate the classes being deserialized, allowing attackers to leverage gadget chains present in the WebLogic Server classpath. These gadget chains can be chained together to achieve arbitrary code execution during the deserialization process.

Java deserialization vulnerabilities occur when an application deserializes untrusted data without proper controls. Certain classes, when combined in specific ways (gadget chains), can be exploited to execute arbitrary commands. WebLogic Server's broad classpath, which includes many utility libraries, provides ample gadget classes for attackers to construct exploitation payloads.

Attack Vector

The attack is conducted remotely over the network, targeting WebLogic Server's T3 or IIOP protocol listeners. An attacker crafts a malicious serialized Java object containing a gadget chain payload (such as those generated by tools like ysoserial) and sends it to the target server. The attack flow typically involves:

1. Reconnaissance: Identifying WebLogic Server instances with exposed T3/IIOP ports (commonly port 7001)
2. Payload Generation: Creating a malicious serialized object using known gadget chains compatible with WebLogic's classpath
3. Exploitation: Sending the crafted payload to the T3/IIOP listener
4. Code Execution: The server deserializes the payload, triggering the gadget chain and executing the attacker's code with the privileges of the WebLogic Server process

The exploitation mechanism leverages the T3 and IIOP protocols to deliver serialized Java objects that contain malicious gadget chains. When the WebLogic Server deserializes these objects, it inadvertently executes the attacker's payload. Technical details and proof-of-concept information are available in the ZDI-20-504 Advisory and the Packet Storm Exploit documentation.

Detection Methods for CVE-2020-2883

Indicators of Compromise

• Unusual network traffic to T3/IIOP ports (typically TCP 7001 or 7002) containing serialized Java object markers such as aced0005 hex signatures
• Unexpected child processes spawned by the WebLogic Server JVM process, particularly shell processes or command interpreters
• Anomalous outbound network connections from the WebLogic Server to unknown or suspicious external IP addresses
• Evidence of ysoserial gadget chain class names in network traffic or server logs

Detection Strategies

• Deploy network intrusion detection rules to identify T3/IIOP protocol traffic containing Java serialization magic bytes (0xac 0xed 0x00 0x05) followed by known malicious class indicators
• Monitor WebLogic Server access logs and security logs for failed deserialization attempts or unexpected exceptions in the Core component
• Implement endpoint detection and response (EDR) solutions to detect anomalous process execution chains originating from the WebLogic Java process
• Utilize SentinelOne's behavioral AI engine to detect post-exploitation activities such as credential harvesting, lateral movement, or persistence establishment

Monitoring Recommendations

• Enable detailed logging for T3 and IIOP protocol handlers within WebLogic Server to capture incoming connection metadata
• Configure SIEM correlation rules to alert on multiple connection attempts to WebLogic ports from single source IPs in short time windows
• Monitor for creation of new files in WebLogic Server directories, particularly webshells or unauthorized JSP files
• Track process lineage from the WebLogic JVM process to detect spawning of command shells or unauthorized executables

How to Mitigate CVE-2020-2883

Immediate Actions Required

• Apply the Oracle Critical Patch Update (CPU) from April 2020 immediately to all affected WebLogic Server instances
• If patching is not immediately possible, disable T3 and IIOP protocols or restrict access to these ports using network firewalls
• Audit all internet-exposed WebLogic Server instances and ensure T3/IIOP ports are not accessible from untrusted networks
• Deploy web application firewall (WAF) rules or network intrusion prevention systems (IPS) with signatures for WebLogic deserialization attacks

Patch Information

Oracle has released security patches addressing CVE-2020-2883 as part of the April 2020 Critical Patch Update. Administrators should download and apply the appropriate patches for their WebLogic Server version from the Oracle Security Alerts page. Given the vulnerability's presence in CISA's Known Exploited Vulnerabilities catalog, patching should be treated as an emergency priority.

Workarounds

• Disable the T3 protocol by configuring connection filters in the WebLogic Server console to block T3 connections from untrusted networks
• Implement network segmentation to ensure WebLogic Server management ports (T3/IIOP) are only accessible from trusted administrative networks
• Configure WebLogic Server's connection filter to restrict incoming T3/IIOP connections to specific trusted IP addresses
• Consider deploying a reverse proxy or load balancer in front of WebLogic that only permits HTTP/HTTPS traffic and blocks direct T3/IIOP access

# Example WebLogic connection filter configuration to restrict T3 access
# Add to WebLogic Server startup properties or via console
# This restricts T3 connections to localhost only
-Dweblogic.security.net.ConnectionFilterImpl=weblogic.security.net.ConnectionFilterImpl
-Dweblogic.security.net.ConnectionFilter.Rules="127.0.0.1 * * allow t3 t3s; * * * deny t3 t3s"