CVE-2020-26945: MyBatis Deserialization Vulnerability

CVE-2020-26945 Overview

CVE-2020-26945 is an insecure deserialization vulnerability affecting MyBatis, a popular Java persistence framework. The vulnerability exists in versions prior to 3.5.6, where the framework mishandles deserialization of object streams. This flaw could allow attackers to execute arbitrary code by supplying maliciously crafted serialized objects to applications using vulnerable MyBatis versions.

Critical Impact

Successful exploitation of this insecure deserialization vulnerability could lead to remote code execution, data theft, or complete system compromise in applications using affected MyBatis versions.

Affected Products

• MyBatis versions prior to 3.5.6
• Applications and frameworks that depend on vulnerable MyBatis versions
• Java applications using MyBatis for database persistence operations

Discovery Timeline

• 2020-10-10 - CVE-2020-26945 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-26945

Vulnerability Analysis

This vulnerability falls into the insecure deserialization category (CWE-502), which represents a critical class of security flaws in Java applications. The vulnerability arises from MyBatis improperly handling the deserialization of object streams without adequate validation or filtering of the incoming data.

Java deserialization vulnerabilities are particularly dangerous because the deserialization process can trigger the execution of arbitrary code embedded within malicious serialized objects. When an application deserializes untrusted data without proper safeguards, attackers can craft gadget chains that execute during the deserialization process, potentially leading to remote code execution.

The network-based attack vector requires high complexity to exploit, as it typically necessitates the attacker having access to endpoints that process serialized data and knowledge of available gadget chains within the application's classpath.

Root Cause

The root cause of CVE-2020-26945 is the improper handling of deserialization operations in MyBatis prior to version 3.5.6. The framework did not implement sufficient validation or filtering mechanisms when processing serialized object streams. This oversight allowed potentially malicious serialized objects to be processed without adequate security checks, enabling attackers to inject harmful payloads that execute during deserialization.

Attack Vector

The attack vector is network-based, requiring an attacker to send crafted serialized data to an application using a vulnerable MyBatis version. The exploitation scenario typically involves:

1. Identifying an application endpoint that processes serialized Java objects
2. Determining available gadget chains in the application's classpath
3. Crafting a malicious serialized payload containing the gadget chain
4. Sending the payload to the vulnerable endpoint
5. The payload executes during deserialization, achieving code execution

For detailed technical information about the vulnerability and the fix, see the GitHub Pull Request #2079 which addresses this issue. The changes between affected and patched versions can be reviewed in the version comparison between 3.5.5 and 3.5.6.

Detection Methods for CVE-2020-26945

Indicators of Compromise

• Unusual serialized Java object payloads in network traffic targeting application endpoints
• Unexpected process spawning or system commands executed by Java application processes
• Anomalous network connections initiated from Java application servers
• Java deserialization-related exceptions in application logs followed by suspicious behavior

Detection Strategies

• Monitor for known Java deserialization attack patterns in network traffic using IDS/IPS signatures
• Implement application-level logging to track deserialization operations and flag suspicious objects
• Use Runtime Application Self-Protection (RASP) solutions to detect exploitation attempts
• Deploy SentinelOne agents to detect and block malicious post-exploitation behavior

Monitoring Recommendations

• Enable verbose logging for MyBatis operations and review logs for deserialization anomalies
• Monitor Java application processes for unexpected child process creation or network activity
• Implement alerting for attempts to deserialize objects from untrusted sources
• Use software composition analysis tools to inventory MyBatis versions across your environment

How to Mitigate CVE-2020-26945

Immediate Actions Required

• Upgrade MyBatis to version 3.5.6 or later immediately
• Conduct an inventory of all applications using MyBatis and prioritize patching based on exposure
• Implement network segmentation to limit exposure of applications using vulnerable versions
• Review application code for endpoints that accept serialized Java objects

Patch Information

The MyBatis development team addressed this vulnerability in version 3.5.6. Organizations should upgrade to this version or later to remediate the vulnerability. The fix can be reviewed in GitHub Pull Request #2079.

To upgrade MyBatis in Maven-based projects, update the dependency version in your pom.xml. For Gradle projects, update the dependency in your build.gradle file. After updating, thoroughly test application functionality to ensure compatibility.

Workarounds

• If immediate patching is not possible, implement deserialization filtering using Java's ObjectInputFilter mechanism
• Restrict network access to applications using vulnerable MyBatis versions to trusted sources only
• Implement Web Application Firewall rules to block known deserialization attack payloads
• Consider implementing a serialization allowlist to restrict which classes can be deserialized

# Configuration example
# Verify MyBatis version in Maven projects
mvn dependency:tree | grep mybatis

# Update pom.xml to use patched version
# <dependency>
#     <groupId>org.mybatis</groupId>
#     <artifactId>mybatis</artifactId>
#     <version>3.5.6</version>
# </dependency>

# For Gradle projects, update build.gradle:
# implementation 'org.mybatis:mybatis:3.5.6'