CVE-2026-42779: Apache Mina RCE Vulnerability

CVE-2026-42779 Overview

CVE-2026-42779 is an unsafe deserialization vulnerability in Apache MINA's AbstractIoBuffer.resolveClass() method. The original fix for CVE-2026-41635 was not backported to the 2.1.X and 2.2.X branches, leaving these versions exposed. The resolveClass() method contains two branches, and the branch handling static classes or primitive types skips the classname allowlist check entirely. Attackers can bypass the deserialization filter and trigger arbitrary code execution through Class.forName(). Affected versions include Apache MINA 2.1.0 through 2.1.11 and 2.2.0 through 2.2.6. Applications calling IoBuffer.getObject() are exposed to remote exploitation.

Critical Impact

Network-reachable applications using vulnerable Apache MINA versions can be exploited for unauthenticated remote code execution through crafted serialized payloads.

Affected Products

• Apache MINA 2.1.0 through 2.1.11
• Apache MINA 2.2.0 through 2.2.6
• Applications using Apache MINA that invoke IoBuffer.getObject()

Discovery Timeline

• 2026-05-01 - CVE-2026-42779 published to NVD
• 2026-05-01 - Last updated in NVD database

Technical Details for CVE-2026-42779

Vulnerability Analysis

The vulnerability is classified under [CWE-502] Deserialization of Untrusted Data. Apache MINA provides IoBuffer.getObject() as a convenience method for reading serialized Java objects from a network buffer. To prevent deserialization gadget attacks, MINA implements a classname allowlist enforced inside AbstractIoBuffer.resolveClass(). The fix shipped for CVE-2026-41635 in earlier branches was never propagated to the 2.1.X and 2.2.X release lines, regressing the security posture of those versions.

When an application calls IoBuffer.getObject() on attacker-controlled input, the unsafe code path resolves classes without enforcing the allowlist. This allows the deserializer to load arbitrary classes available on the classpath, enabling gadget chain exploitation patterns commonly seen in libraries like Apache Commons Collections.

Root Cause

The resolveClass() implementation contains two distinct code paths. One path handles regular class descriptors and consults the accepted class filter. The second path, used for static classes or primitive types, calls Class.forName() directly without consulting the allowlist. The patch in versions 2.1.12 and 2.2.7 applies the classname allowlist earlier in the resolution flow, ensuring both branches enforce the filter before any class loading occurs.

Attack Vector

Exploitation requires no authentication and no user interaction. An attacker sends a crafted serialized object stream to a network endpoint backed by Apache MINA where the application invokes IoBuffer.getObject(). The deserializer resolves a malicious gadget class, triggering side effects during object reconstruction that culminate in arbitrary code execution within the JVM process. Because Apache MINA is commonly used in protocol servers, exposure typically aligns with internet-facing or intranet-facing service ports.

Detection Methods for CVE-2026-42779

Indicators of Compromise

• Unexpected child processes spawned by Java processes hosting Apache MINA services, particularly shell interpreters or scripting engines.
• Outbound network connections from MINA-backed services to unfamiliar hosts immediately following inbound traffic spikes.
• Java stack traces in application logs referencing AbstractIoBuffer.resolveClass alongside unfamiliar class names.
• Inbound traffic containing the Java serialization magic bytes AC ED 00 05 to ports served by MINA applications.

Detection Strategies

• Inventory all Java applications and identify dependencies on org.apache.mina:mina-core versions in the affected ranges.
• Inspect source code and bytecode for usage of IoBuffer.getObject() to determine real exploitability of each deployment.
• Deploy network signatures matching Java serialization headers on ports hosting MINA-based protocols.

Monitoring Recommendations

• Monitor JVM process behavior for anomalous child process creation, file writes, and outbound connections from MINA service accounts.
• Enable verbose deserialization logging where supported and forward events to a centralized analytics platform.
• Alert on classloading of high-risk classes such as Runtime, ProcessBuilder, or known gadget chain classes within MINA-hosted JVMs.

How to Mitigate CVE-2026-42779

Immediate Actions Required

• Upgrade Apache MINA to version 2.1.12 or 2.2.7 depending on the branch in use.
• Audit all applications for calls to IoBuffer.getObject() and prioritize patching network-exposed services first.
• Remove unused gadget-prone dependencies from the classpath of MINA applications, including legacy Commons Collections versions.

Patch Information

The Apache MINA project resolved the issue in versions 2.1.12 and 2.2.7 by applying the classname allowlist earlier in AbstractIoBuffer.resolveClass(), ensuring the static class and primitive type branch is also subject to filter enforcement. Refer to the Apache Security List Post for vendor guidance.

Workarounds

• Restrict the classname allowlist passed to MINA's deserialization filter to the minimum set of trusted classes required by the application.
• Place network filtering controls in front of MINA-backed services to limit exposure to trusted clients only.
• Where feasible, replace IoBuffer.getObject() usage with a safer serialization format such as JSON or Protocol Buffers.

# Maven dependency upgrade example
# Update pom.xml to a fixed Apache MINA release
# <dependency>
#   <groupId>org.apache.mina</groupId>
#   <artifactId>mina-core</artifactId>
#   <version>2.2.7</version>
# </dependency>
mvn versions:set-property -Dproperty=mina.version -DnewVersion=2.2.7
mvn dependency:tree | grep mina-core