CVE-2018-12247 in mruby
Summary
by MITRE
An issue was discovered in mruby 1.4.1. There is a NULL pointer dereference in mrb_class, related to certain .clone usage, because mrb_obj_clone in kernel.c copies flags other than the MRB_FLAG_IS_FROZEN flag (e.g., the embedded flag).
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Analysis
by VulDB Data Team • 03/22/2023
The vulnerability identified as CVE-2018-12247 represents a critical NULL pointer dereference flaw within the mruby scripting engine version 1.4.1. This issue manifests specifically during object cloning operations when the mrb_obj_clone function in kernel.c fails to properly handle certain flag copying behaviors. The flaw occurs when the cloning process attempts to copy flags including the embedded flag, which creates a scenario where subsequent operations may reference a null memory location, leading to potential application crashes or system instability.
The technical root cause of this vulnerability stems from improper flag management during object cloning within the mruby runtime environment. When the mrb_obj_clone function processes objects, it indiscriminately copies various flags without proper validation of the target object's state. The embedded flag in particular becomes problematic because it indicates whether an object is embedded within another object structure, and when this flag is incorrectly copied or maintained during cloning, it can result in a null pointer dereference. This behavior aligns with CWE-476 which catalogs null pointer dereference vulnerabilities, and specifically demonstrates how improper flag handling can create memory access violations. The vulnerability is particularly concerning because it occurs in the core kernel operations of the scripting engine, making it exploitable during normal runtime execution.
The operational impact of CVE-2018-12247 extends beyond simple application crashes to potentially enable more serious security consequences. When an attacker can trigger this NULL pointer dereference through crafted clone operations, they may cause denial of service conditions that can disrupt legitimate system operations. In environments where mruby is embedded within larger applications or services, this vulnerability could allow an attacker to destabilize critical processes or potentially create conditions that might be leveraged for further exploitation. The vulnerability affects the fundamental object cloning mechanism, which is a common operation in scripting environments, meaning that any application relying on mruby's clone functionality could be impacted. This aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, as the null pointer dereference can effectively crash services that depend on mruby.
Mitigation strategies for CVE-2018-12247 should focus on immediate patching of affected mruby installations to version 1.4.2 or later, which contains the necessary fixes for proper flag handling during object cloning. System administrators should conduct comprehensive vulnerability assessments to identify all applications and services that utilize mruby, particularly those that may be vulnerable to crafted clone operations. Additionally, implementing input validation and sanitization measures can help reduce the attack surface by preventing malicious clone operations from reaching the vulnerable code paths. Organizations should also consider monitoring for unusual application behavior or crashes that might indicate exploitation attempts, as the null pointer dereference may manifest as intermittent service disruptions or application crashes. The fix implemented in subsequent versions addresses the core issue by ensuring that the embedded flag and other relevant flags are properly handled during the cloning process, preventing the NULL pointer dereference condition that was previously possible.