CVE-2016-2337 in Ruby
Summary
by MITRE
Type confusion exists in _cancel_eval Ruby's TclTkIp class method. Attacker passing different type of object than String as "retval" argument can cause arbitrary code execution.
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Analysis
by VulDB Data Team • 04/20/2025
The vulnerability identified as CVE-2016-2337 represents a critical type confusion flaw within Ruby's TclTkIp class method, specifically in the _cancel_eval function. This issue arises from inadequate type validation during object processing, creating a scenario where the application fails to properly handle type mismatches between expected and actual data inputs. The vulnerability manifests when an attacker supplies an object of a different type than the anticipated String parameter for the "retval" argument, which fundamentally undermines the application's type safety mechanisms. Such type confusion vulnerabilities are particularly dangerous because they can lead to unpredictable program behavior and potentially enable remote code execution through carefully crafted malicious inputs.
The technical implementation of this vulnerability stems from Ruby's dynamic typing nature combined with insufficient input validation in the TclTkIp class implementation. When the _cancel_eval method processes the retval parameter, it assumes the argument will be a String object and proceeds with operations that are specifically designed for string manipulation. However, when an attacker provides an object of a different type such as an Integer, Array, or custom object, the method's internal logic becomes confused about the object's expected interface and behavior. This type confusion allows the attacker to manipulate the execution flow by exploiting the difference between how the system expects to handle string objects versus other object types. The flaw essentially creates a situation where the program's memory management and execution context can be manipulated through type-based attacks, which aligns with CWE-471: "Direct Use of Unsafe Variable" and CWE-128: "Unsigned to Signed Conversion Error" in the CWE classification system.
The operational impact of this vulnerability extends beyond simple denial of service to encompass full arbitrary code execution capabilities. Attackers can leverage this type confusion to inject malicious payloads that exploit the underlying memory corruption patterns inherent in Ruby's object model. When the system attempts to process the unexpected object type, it can cause stack corruption, heap manipulation, or other memory-related vulnerabilities that enable attackers to execute arbitrary instructions with the privileges of the affected Ruby process. This vulnerability affects systems running Ruby versions that include the affected TclTkIp class, particularly those that utilize Tk-based graphical interfaces or Tcl integration components. The attack vector is typically remote, as the vulnerability can be triggered through network-based inputs or file processing operations that pass data to the vulnerable method.
Mitigation strategies for CVE-2016-2337 require immediate patching of affected Ruby installations to address the root cause of the type confusion issue. System administrators should prioritize updating to Ruby versions that contain the patched TclTkIp implementation and ensure all dependencies are current with security fixes. Additionally, input validation should be strengthened at all boundaries where TclTkIp methods are called, particularly around the retval parameter handling. Implementing proper type checking and explicit type conversion before method invocation can prevent the type confusion from occurring in the first place. Network segmentation and access controls should be enforced to limit exposure to potential attackers, while monitoring systems should be configured to detect unusual patterns in TclTkIp method calls. The vulnerability also highlights the importance of following secure coding practices such as those outlined in the OWASP Secure Coding Guidelines and aligns with ATT&CK technique T1059.007: "Command and Scripting Interpreter: PowerShell" when attackers leverage such vulnerabilities to execute malicious payloads through compromised Ruby applications. Organizations should conduct thorough code reviews focusing on dynamic type handling and ensure that all object-oriented programming practices properly validate input types before processing.