CVE-2016-2339 in Ruby
Summary
by MITRE
An exploitable heap overflow vulnerability exists in the Fiddle::Function.new "initialize" function functionality of Ruby. In Fiddle::Function.new "initialize" heap buffer "arg_types" allocation is made based on args array length. Specially constructed object passed as element of args array can increase this array size after mentioned allocation and cause heap overflow.
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Analysis
by VulDB Data Team • 04/20/2025
The vulnerability described in CVE-2016-2339 represents a critical heap overflow condition within Ruby's Fiddle library, specifically affecting the Fiddle::Function.new initialize method. This flaw resides in the memory management mechanism responsible for handling foreign function interface operations, which allows Ruby programs to call functions in shared libraries. The issue manifests when the system allocates memory for argument types based on an initial assessment of the arguments array size, creating a scenario where subsequent modifications to the array can lead to memory corruption.
The technical implementation of this vulnerability stems from improper bounds checking during heap allocation procedures within the Fiddle::Function class initialization process. When Ruby processes function definitions through the Fiddle::Function.new constructor, it first determines the size of the argument array and subsequently allocates a buffer named arg_types to store type information for each parameter. However, the code fails to account for potential modifications to the arguments array between the initial size determination and the actual buffer allocation, creating a window where an attacker can manipulate the array contents to cause a buffer overflow condition.
The operational impact of this vulnerability extends beyond typical memory corruption scenarios, as it enables remote code execution under specific conditions. Attackers can craft malicious objects that, when passed as elements in the arguments array, cause the system to allocate insufficient memory while simultaneously allowing the array to grow beyond its allocated bounds. This creates a situation where subsequent writes to the buffer can overwrite adjacent memory regions, potentially corrupting critical program data structures or even allowing execution of arbitrary code. The vulnerability specifically targets the Ruby interpreter's heap management and can be exploited through carefully constructed input that manipulates the array size after initial allocation.
This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and also demonstrates characteristics of CWE-787, representing out-of-bounds write vulnerabilities. From an ATT&CK framework perspective, this represents a privilege escalation vector through code injection techniques, potentially classified under T1059 for command and scripting interpreter usage and T1068 for exploit for privilege escalation. The attack surface is particularly concerning for Ruby applications that process untrusted input through Fiddle::Function.new calls, as it allows for arbitrary code execution without requiring elevated privileges. Mitigation strategies should focus on updating to patched Ruby versions, implementing input validation for Fiddle function calls, and employing address space layout randomization to reduce exploit reliability. Additionally, application developers should avoid passing untrusted objects through Fiddle function definitions and consider implementing additional bounds checking mechanisms in their code to prevent similar issues in custom implementations.