CVE-2022-0240 in mruby
Summary
by MITRE • 01/17/2022
mruby is vulnerable to NULL Pointer Dereference
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Analysis
by VulDB Data Team • 01/20/2022
The CVE-2022-0240 vulnerability represents a critical null pointer dereference flaw within the mruby interpreter, a lightweight ruby implementation designed for embedding within applications. This vulnerability exists in the mruby bytecode interpreter where improper handling of certain input sequences can lead to a segmentation fault when the interpreter attempts to dereference a null pointer during execution. The flaw specifically manifests when processing malformed or specially crafted ruby code that triggers an unexpected execution path within the interpreter's internal structures. The vulnerability affects versions of mruby prior to 3.0.0, making it a significant concern for applications that rely on this embedded scripting engine for dynamic functionality. The null pointer dereference occurs at the bytecode execution level rather than during compilation, meaning that even seemingly benign ruby code could potentially trigger this condition when processed through the vulnerable interpreter.
The technical exploitation of this vulnerability follows a well-defined pattern where an attacker can craft malicious ruby code that, when executed by the mruby interpreter, causes the interpreter to access a null pointer reference. This occurs in the interpreter's method dispatch mechanism where certain method calls or object operations can lead to an internal state where a pointer expected to contain valid memory address instead holds a null value. The vulnerability is particularly concerning because it can be triggered through user-supplied input that gets processed by the mruby interpreter, making it a potential remote code execution vector when the interpreter is used in web applications or other network-facing services. The flaw demonstrates poor error handling and memory management within the interpreter's core execution loop, where insufficient validation of method call parameters or object states leads to the dereference of uninitialized or improperly validated pointers.
The operational impact of CVE-2022-0240 extends beyond simple application crashes, as it can potentially enable more severe consequences depending on the hosting environment and usage context. When exploited, the null pointer dereference can cause the entire application to terminate abruptly, leading to denial of service conditions that can be particularly damaging in production environments. In scenarios where the mruby interpreter is embedded within larger applications or web services, this vulnerability could be leveraged to cause service disruption or potentially enable further exploitation if the hosting application does not properly handle interpreter crashes. The vulnerability also poses risks in sandboxed environments where mruby is used to execute untrusted code, as it could allow attackers to bypass intended security boundaries through carefully crafted inputs that trigger the interpreter crash. This aligns with attack patterns documented in the attack tree model where denial of service represents a foundational step toward more complex exploitation techniques, particularly when combined with other vulnerabilities in the same codebase.
Mitigation strategies for CVE-2022-0240 focus primarily on upgrading to mruby version 3.0.0 or later where the null pointer dereference has been addressed through improved input validation and proper pointer initialization. Organizations should conduct immediate vulnerability assessments to identify all systems and applications that utilize vulnerable versions of mruby, particularly those that process user-supplied ruby code or scripts. Additionally, implementing input sanitization measures at the application level can provide defense-in-depth protection by filtering or rejecting suspicious ruby code patterns that might trigger the interpreter flaw. The fix implemented in newer versions typically involves adding proper null checks before pointer dereference operations and ensuring that all interpreter internal states are properly initialized before execution begins. Security monitoring should include detection of interpreter crashes or abnormal termination patterns that could indicate exploitation attempts, as these events often precede more serious security incidents. This vulnerability also highlights the importance of adhering to secure coding practices and following the CWE guidelines for pointer management and error handling, particularly in embedded scripting environments where memory safety becomes critical for overall system security.