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:

Identifying an application endpoint that processes serialized Java objects
Determining available gadget chains in the application's classpath
Crafting a malicious serialized payload containing the gadget chain
Sending the payload to the vulnerable endpoint
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

bash

# 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'