CVE-2021-32824: Apache Dubbo vulnerable to remote code execution via Telnet Handler

Apache Dubbo is a Java based, open source RPC framework. Versions prior to 2.6.10 and 2.7.10 are vulnerable to pre-authorization remote code execution via arbitrary bean manipulation in the Telnet handler. The Dubbo main service port can be used to access a Telnet Handler which offers some basic methods to collect information about the providers and methods exposed by the service and it can even allow to shutdown the service. This endpoint is unprotected.

Additionally, a provider method can be invoked using the invoke handler. This handler uses a safe version of FastJson to process the call arguments. However, the resulting list is later processed with PojoUtils.realize which can be used to instantiate arbitrary classes and invoke its setters. Even though FastJson is properly protected with a default blocklist, PojoUtils.realize is not, and an attacker can leverage that to achieve remote code execution.

Versions 2.6.10 and 2.7.10 contain fixes for this issue.