CVE-2018-10191 in mruby
Summary
by MITRE
In versions of mruby up to and including 1.4.0, an integer overflow exists in src/vm.c::mrb_vm_exec() when handling OP_GETUPVAR in the presence of deep scope nesting, resulting in a use-after-free. An attacker that can cause Ruby code to be run can use this to possibly execute arbitrary code.
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Analysis
by VulDB Data Team • 02/28/2023
The vulnerability CVE-2018-10191 represents a critical integer overflow flaw in mruby versions 1.4.0 and earlier, specifically within the virtual machine execution engine. This issue manifests in the src/vm.c file during processing of the OP_GETUPVAR operation, which is responsible for accessing variables from enclosing scopes. The vulnerability becomes particularly dangerous when dealing with deeply nested scope structures, where the integer overflow corrupts memory management operations.
The technical implementation of this flaw occurs in the mrb_vm_exec() function where the interpreter processes bytecode operations. When encountering deeply nested scopes, the calculation of variable indices fails to properly validate integer boundaries, leading to an overflow condition. This overflow corrupts the memory layout of the interpreter's internal data structures, specifically affecting the reference counting mechanism used for garbage collection. The corrupted state creates a use-after-free condition where freed memory blocks are accessed and potentially overwritten, providing an attacker with a path to arbitrary code execution.
From an operational perspective, this vulnerability presents a severe risk to any system running mruby versions up to 1.4.0, particularly in environments where user-provided code execution is permitted. The attack vector requires an attacker to be able to inject and execute Ruby code within the target environment, which could occur through web applications, scripting interfaces, or any application that utilizes mruby for embedded scripting. The use-after-free condition allows for memory corruption that can be leveraged to redirect program execution flow, making this a remote code execution vulnerability with significant impact potential.
The vulnerability maps to CWE-190, Integer Overflow or Wraparound, and specifically relates to CWE-416 Use After Free, as the integer overflow directly leads to memory corruption that enables use-after-free exploitation patterns. From an ATT&CK framework perspective, this vulnerability aligns with T1059.007 Command and Scripting Interpreter: Ruby, and T1203 Exploitation for Client Execution, representing a post-compromise execution capability. The vulnerability affects the integrity and availability of the target system, as successful exploitation can result in complete system compromise. Organizations should immediately upgrade to mruby version 1.4.1 or later, which includes proper integer bounds checking and memory management fixes. Additional mitigations include implementing strict input validation, sandboxing mruby execution environments, and monitoring for suspicious code execution patterns in applications that utilize this interpreter.