Introduction to FasterXML Jackson
FasterXML Jackson is a data processing tool built for Java from an American company FasterXML. Jackson-databind is one of its components with data binding. The component can convert Java objects to json objects, as well as converting json to Java objects.
NVD released information about FasterXML Jackson-databind remote code execution vulnerability on March 2, 2020 with CVE number: CVE-2020-9548. The vulnerability is caused by JNDI injection, which leads to remote code execution. Jackson-databind version 2.0.0 - 188.8.131.52 lack the br.com.anteros.dbcp.AnterosDBCPConfig blacklist. Attackers can use flaws to bypass restrictions, perform JNDI injection, then execute arbitrary code on the infected host eventually.
Taking Jackson-databind 2.10.1 + Anteros-DBCP-1.0.1 + metrics-healthchecks-3.0.2 as the vulnerability environment for analysis, Jackson-databind will perform internal initialization. After that, we will process the json data we passed in. The vulnerability mainly exists in the br.com.anteros.dbcp.AnterosDBCPConfig class in the Anteros-DBCP library Let's track the process of exploiting the vulnerability. When Jackson-databind receives a piece of json data, it will parse the Json data in the ReaderBasedJsonParser class and check the character one by one. As shown below:
We use double quotes to determine the start and end of the field name. The class obtained by parsing the json data will be instantiated in the call method, and the internal member variables will be initialized when the constructor is called.
We obtain the field names in the incoming json data, and assign values to internal attributes through deserialization.
We call methods in the class through reflection. When the getObjectOrPerformJndiLookup method in the br.com.anteros.dbcp.AnterosDBCPConfig class is executed , the victim host will access the malicious link passed by the attacker and load a malicious file, thereby triggering a remote code execution attack. It has been verified that both the metricRegistry and healthCheckRegistry attributes can be used to exploit the vulnerability.
We set up Jackson-databind 2.10.1 + Anteros-DBCP-1.0.1 + metrics-healthchecks-3.0.2 environment, pass in specially constructed json data, and let the target server load malicious files on the remote host to execute arbitrary code on the host. as shown in figure:
Jackson-databind 2.0.0 - 184.108.40.206
Mar 2, 2020 Sangfor FarSight Labs detected FasterXML Jackson-databind remote code execution vulnerability CVE-2020-9548.
Mar 4, 2020 Sangfor FarSight Labs reproduced this vulnerability successfully, then released alerts and solutions.
The official has fixed this vulnerability. Please visit the following link to download the latest version:
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