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: true
enable_scripted_user_defined_functions: true
enable_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)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.