CVE-2024-46983: Antfin Sofa-hessian RCE Vulnerability

CVE-2024-46983 Overview

CVE-2024-46983 is an insecure deserialization vulnerability in sofa-hessian, an internal improved version of Hessian3/4 serialization protocol powered by Ant Group CO., Ltd. The vulnerability allows attackers to bypass the SOFA Hessian blacklist protection mechanism through a gadget chain that relies solely on JDK components, potentially leading to remote code execution without requiring any third-party dependencies.

Critical Impact

This vulnerability enables complete bypass of the deserialization blacklist protection, allowing unauthenticated remote attackers to execute arbitrary code on affected systems through a JDK-only gadget chain.

Affected Products

• Antfin sofa-hessian versions prior to 3.5.5

Discovery Timeline

• September 19, 2024 - CVE-2024-46983 published to NVD
• September 25, 2024 - Last updated in NVD database

Technical Details for CVE-2024-46983

Vulnerability Analysis

The SOFA Hessian protocol implements a blacklist-based security mechanism designed to prevent deserialization of known dangerous classes that could be exploited for malicious purposes. However, researchers identified a gadget chain that successfully bypasses this blacklist protection entirely using only classes available within the standard Java Development Kit (JDK).

This represents a significant security weakness because blacklist-based approaches are inherently incomplete—they can only block known dangerous classes, leaving room for novel attack vectors. The JDK-only nature of this gadget chain makes it particularly concerning as it requires no additional third-party libraries to be present on the target system, dramatically increasing the attack surface.

The vulnerability is classified under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component) and relates to insecure deserialization, which is consistently ranked among the most critical web application security risks.

Root Cause

The root cause lies in the incomplete nature of the blacklist mechanism used to filter dangerous classes during deserialization. While the blacklist approach attempts to enumerate and block known dangerous classes, it fails to account for all possible gadget chains that can be constructed using JDK-native classes. The discovered gadget chain exploits classes that were not included in the blacklist, allowing attackers to craft malicious serialized objects that bypass security controls entirely.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction to exploit. An attacker can craft a malicious serialized payload containing the JDK-based gadget chain and send it to any endpoint that processes SOFA Hessian deserialization. Upon processing, the malicious payload bypasses the blacklist validation and triggers arbitrary code execution on the target system.

The exploitation typically follows this pattern:

1. Attacker identifies an application using vulnerable sofa-hessian for deserialization
2. Attacker constructs a serialized payload using the JDK-only gadget chain
3. The malicious payload is sent to the target application via network request
4. SOFA Hessian attempts to deserialize the payload and checks against the blacklist
5. The gadget chain classes are not in the blacklist, so deserialization proceeds
6. Code execution is triggered through the gadget chain mechanism

Detection Methods for CVE-2024-46983

Indicators of Compromise

• Unexpected network connections originating from Java processes handling Hessian deserialization
• Anomalous process spawning from Java application servers
• Suspicious serialized data patterns in network traffic targeting Hessian endpoints
• Unusual file system activity or modifications following Hessian protocol interactions

Detection Strategies

• Monitor for unusual Java class loading patterns, particularly classes commonly used in deserialization gadget chains
• Implement network intrusion detection rules to identify malformed or suspicious Hessian protocol traffic
• Enable verbose logging for deserialization operations to capture attempted exploitation
• Deploy application-level monitoring to detect unexpected code execution patterns

Monitoring Recommendations

• Configure alerts for processes spawning from Java application servers
• Monitor outbound network connections from systems running sofa-hessian
• Track changes to serialization blacklist configuration files
• Implement runtime application self-protection (RASP) to detect deserialization attacks

How to Mitigate CVE-2024-46983

Immediate Actions Required

• Upgrade sofa-hessian to version 3.5.5 or later immediately
• Review all applications using sofa-hessian for potential exposure
• Implement network segmentation to limit exposure of vulnerable services
• Consider temporarily disabling Hessian deserialization endpoints if upgrade is not immediately possible

Patch Information

Ant Group has addressed this vulnerability by updating the deserialization blacklist in sofa-hessian version 3.5.5. The updated blacklist includes the classes used in the JDK-only gadget chain, preventing exploitation of this specific attack vector. Organizations should upgrade to this version as soon as possible.

For detailed information about the security fix, refer to the GitHub Security Advisory.

Workarounds

• Maintain a custom blacklist in the directory external/serialize.blacklist with additional dangerous classes
• Implement allowlist-based deserialization filtering as a more robust defense mechanism
• Deploy Web Application Firewall (WAF) rules to filter suspicious Hessian protocol traffic
• Restrict network access to Hessian deserialization endpoints to trusted sources only

# Configuration example - Custom blacklist maintenance
# Create or update the external serialization blacklist file
mkdir -p external
# Add known dangerous classes to the blacklist
# Note: Consult security advisories for specific classes to add
echo "# Custom serialization blacklist" > external/serialize.blacklist
echo "# Add dangerous classes one per line" >> external/serialize.blacklist