CVE-2026-41635: Apache Mina RCE Vulnerability

CVE-2026-41635 Overview

CVE-2026-41635 is an insecure deserialization vulnerability in Apache MINA's AbstractIoBuffer.resolveClass() method. The vulnerability exists because the method contains two branches for resolving classes, and one branch—specifically handling static classes or primitive types—fails to validate against the classname allowlist. This bypass allows attackers to execute arbitrary code remotely by deserializing malicious objects through applications that call IoBuffer.getObject().

Critical Impact

Remote attackers can bypass the classname allowlist protection mechanism to execute arbitrary code on vulnerable Apache MINA applications without authentication.

Affected Products

• Apache MINA 2.0.0 through 2.0.27
• Apache MINA 2.1.0 through 2.1.10
• Apache MINA 2.2.0 through 2.2.5

Discovery Timeline

• April 27, 2026 - CVE-2026-41635 published to NVD
• April 29, 2026 - Last updated in NVD database

Technical Details for CVE-2026-41635

Vulnerability Analysis

This insecure deserialization vulnerability (CWE-502) stems from an incomplete security control implementation in Apache MINA's buffer handling mechanism. When IoBuffer.getObject() is invoked, the underlying AbstractIoBuffer.resolveClass() method is responsible for validating classes during the deserialization process. The method was designed to check incoming class names against an allowlist to prevent unauthorized class instantiation.

However, the implementation contains a critical flaw: when handling static classes or primitive types, the method bypasses the allowlist check entirely before calling Class.forName(). This creates an exploitation window where attackers can craft serialized payloads that trigger the vulnerable code path, circumventing the intended security control and achieving arbitrary code execution.

Root Cause

The root cause is an incomplete implementation of the classname allowlist validation in AbstractIoBuffer.resolveClass(). The method has conditional branching logic where one branch (handling static classes or primitive types) does not invoke the class filter validation, directly calling Class.forName() without any security checks. This architectural flaw allows malicious serialized objects to bypass the intended access control mechanism.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying an application using Apache MINA that processes user-controlled serialized data
2. Crafting a malicious serialized object that triggers the vulnerable code path in resolveClass()
3. Sending the payload to the target application's network endpoint
4. The vulnerable branch processes the payload without allowlist validation
5. Class.forName() instantiates the attacker-controlled class, resulting in arbitrary code execution

The vulnerability manifests in the AbstractIoBuffer.resolveClass() method where class resolution bypasses the security filter. When a serialized object is received and IoBuffer.getObject() is called, the method fails to apply the classname allowlist for certain class types, allowing arbitrary class instantiation. Refer to the Apache Mailing List Thread for detailed technical information about the fix implementation.

Detection Methods for CVE-2026-41635

Indicators of Compromise

• Unexpected outbound network connections from application servers running Apache MINA
• Anomalous process spawning from Java processes using MINA libraries
• Unusual serialized object payloads in network traffic containing non-standard class references
• Log entries indicating deserialization errors or unexpected class loading attempts

Detection Strategies

• Monitor network traffic for suspicious serialized Java objects targeting MINA-based services
• Implement application-level logging around IoBuffer.getObject() calls to capture class resolution attempts
• Deploy Java deserialization attack detection rules in WAF/IDS systems
• Use runtime application self-protection (RASP) solutions to detect unauthorized class loading

Monitoring Recommendations

• Enable verbose logging for Apache MINA buffer operations in production environments
• Configure alerts for unexpected class loading patterns in JVM monitoring tools
• Monitor memory and CPU usage anomalies that may indicate exploitation attempts
• Review application logs for deserialization-related exceptions or errors

How to Mitigate CVE-2026-41635

Immediate Actions Required

• Upgrade Apache MINA to version 2.0.28, 2.1.11, or 2.2.6 immediately based on your current branch
• Audit applications to identify all instances where IoBuffer.getObject() is called
• Implement network segmentation to limit exposure of MINA-based services
• Review and restrict network access to services using affected Apache MINA versions

Patch Information

The vulnerability is resolved in Apache MINA versions 2.0.28, 2.1.11, and 2.2.6. The fix applies the classname allowlist validation earlier in the resolveClass() method, ensuring all code paths perform the security check before calling Class.forName(). Organizations should upgrade to the appropriate fixed version based on their current MINA branch. For detailed patch information, refer to the Apache Mailing List Thread.

Workarounds

• If immediate patching is not possible, restrict network access to services using IoBuffer.getObject()
• Implement additional input validation layers before data reaches MINA deserialization
• Consider using application firewalls to filter potentially malicious serialized payloads
• Disable or remove unnecessary IoBuffer.getObject() functionality where possible

# Configuration example - Verify Apache MINA version
mvn dependency:tree | grep mina

# Update Maven dependency to patched version (example for 2.2.x branch)
# In pom.xml, update to:
# <dependency>
#     <groupId>org.apache.mina</groupId>
#     <artifactId>mina-core</artifactId>
#     <version>2.2.6</version>
# </dependency>