CVE-2020-1959 in Syncope
Summary
by MITRE
A Server-Side Template Injection was identified in Apache Syncope prior to 2.1.6 enabling attackers to inject arbitrary Java EL expressions, leading to an unauthenticated Remote Code Execution (RCE) vulnerability. Apache Syncope uses Java Bean Validation (JSR 380) custom constraint validators. When building custom constraint violation error messages, they support different types of interpolation, including Java EL expressions. Therefore, if an attacker can inject arbitrary data in the error message template being passed, they will be able to run arbitrary Java code.
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Analysis
by VulDB Data Team • 05/04/2020
The vulnerability CVE-2020-1959 represents a critical server-side template injection flaw in Apache Syncope versions prior to 2.1.6 that fundamentally compromises the security posture of the system. This issue stems from the improper handling of user-supplied data within custom constraint violation error messages, creating a pathway for attackers to execute arbitrary Java code without authentication. The vulnerability specifically targets the Java Bean Validation implementation (JSR 380) which Apache Syncope employs for custom constraint validators, making it particularly dangerous as it leverages the core validation framework that many security controls depend upon.
The technical exploitation of this vulnerability occurs through the manipulation of error message templates that support Java Expression Language (EL) interpolation. When Apache Syncope processes custom constraint violations, it allows for dynamic message generation that includes support for EL expressions, enabling attackers to inject malicious code within the error message context. This design flaw means that any input field that can influence constraint violation messages becomes a potential attack vector, as the system does not properly sanitize or escape user-provided data before incorporating it into the template processing pipeline. The vulnerability maps directly to CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')" and specifically addresses the dangerous combination of template injection with Java EL expression evaluation.
The operational impact of this vulnerability extends far beyond simple data compromise, as it enables unauthenticated remote code execution that can be exploited by attackers to gain complete control over the affected server. An attacker can leverage this vulnerability to execute arbitrary Java code with the privileges of the application server, potentially leading to full system compromise, data exfiltration, and lateral movement within the network. The lack of authentication requirements makes this vulnerability particularly dangerous as it can be exploited from any network location, and the RCE capability allows for persistent backdoor installation, system enumeration, and further attack progression. This vulnerability directly aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: Java" and T1078.004 for "Valid Accounts: Valid Accounts" since attackers can leverage legitimate Java processes to execute malicious code.
Organizations using Apache Syncope versions prior to 2.1.6 face significant risk from this vulnerability, as it provides attackers with a straightforward path to system compromise. The vulnerability's exploitation requires no specialized tools beyond standard network reconnaissance and HTTP request manipulation, making it accessible to attackers of varying skill levels. Remediation efforts should focus on upgrading to Apache Syncope 2.1.6 or later, which includes proper input sanitization and escaping mechanisms for constraint violation messages. Additional mitigations include implementing network segmentation, monitoring for unusual Java process activity, and deploying web application firewalls that can detect and block malicious EL expression patterns. Security teams should also conduct comprehensive vulnerability assessments to identify any custom constraint validators that may have similar template injection vulnerabilities, as this flaw could potentially exist in other applications utilizing similar validation frameworks. The vulnerability demonstrates the critical importance of secure template processing and input validation in enterprise security systems, particularly those handling user-supplied data through validation mechanisms.