Experts disclose details of Apache Cassandra DB RCE

Researchers disclose a now-patched remote code execution (RCE) vulnerability in the Apache Cassandra database software.

JFrog researchers publicly disclosed details of a now-patched high-severity security vulnerability (CVE-2021-44521) in Apache Cassandra database software that could be exploited by remote attackers to achieve code execution on affected installations.

Apache Cassandra is an open-source NoSQL distributed database used by thousands of companies.

“JFrog’s Security Research team recently disclosed an RCE (remote code execution) issue in Apache Cassandra, which has been assigned to CVE-2021-44521 (CVSS 8.4).” reads the analsyis published by JFrog. “This Apache security vulnerability is easy to exploit and has the potential to wreak havoc on systems, but luckily only manifests in non-default configurations of Cassandra.”

Cassandra offers the functionality of creating user-defined-functions (UDFs) that allow to perform custom processing of data in the database.

Admins can use Java and JavaScript to write UDFs. In JavaScript it leverages the Nashorn engine in the Java Runtime Environment (JRE) which is not guaranteed to be secure when accepting untrusted code

JFrog researchers that discovered that when the configuration for user-defined functions (UDFs) are enabled, threat actors could leverage the Nashorn engine to escape the sandbox and achieve remote code execution.

“For example, running the following Nashorn JavaScript code allows execution of an arbitrary shell command –

java.lang.Runtime.getRuntime().exec("touch hacked")

Cassandra’s development team decided to implement a custom sandbox around the UDF execution which uses two mechanisms to restrict the UDF code” states the report.“

Experts noticed that the exploitation is possible when the cassandra.yaml configuration file contains the following definitions:

enable_user_defined_functions: trueenable_scripted_user_defined_functions: trueenable_user_defined_functions_threads: false

“When the option is set to false, all invoked UDF functions run in the Cassandra daemon thread, which has a security manager with some permissions. We will show how to abuse these permissions to achieve sandbox escape and RCE.” continues the analysis.

Experts shared a PoC to create a new file named “hacked” on the Cassandra server

Apache released versions 3.0.26, 3.11.12, and 4.0.2 to address the vulnerability, it adds a new flag “allow_extra_insecure_udfs” that’s set to false by default, it prevents turning off the security manager and blocks access to java.lang.System..

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Pierluigi Paganini

(SecurityAffairs – hacking, RCE)