CVE-2018-14337 in mruby
Summary
by MITRE
The CHECK macro in mrbgems/mruby-sprintf/src/sprintf.c in mruby 1.4.1 contains a signed integer overflow, possibly leading to out-of-bounds memory access because the mrb_str_resize function in string.c does not check for a negative length.
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Analysis
by VulDB Data Team • 04/09/2023
The vulnerability identified as CVE-2018-14337 resides within the mruby scripting engine version 1.4.1, specifically in the mruby-sprintf gem implementation. This flaw manifests through a critical signed integer overflow condition that occurs within the CHECK macro located in the sprintf.c source file. The vulnerability represents a classic software security issue that can potentially lead to arbitrary code execution or system compromise when exploited properly. The affected component operates as part of the string formatting functionality that is fundamental to many applications leveraging mruby as their embedded scripting engine. The flaw demonstrates poor input validation and boundary checking mechanisms that are essential for preventing memory corruption vulnerabilities.
The technical root cause stems from the interaction between the CHECK macro and the mrb_str_resize function in the string.c file. When processing string formatting operations, the CHECK macro performs arithmetic operations that can result in signed integer overflow conditions. This overflow occurs when a calculation produces a value that exceeds the maximum representable value for a signed integer type, causing the value to wrap around to a negative number. The subsequent mrb_str_resize function fails to validate whether the calculated length parameter is negative before proceeding with memory allocation operations, creating a scenario where negative length values can be passed to memory management functions. This design flaw allows attackers to manipulate input parameters to trigger the overflow condition and subsequently cause out-of-bounds memory access patterns.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling attackers to execute arbitrary code within the context of the mruby interpreter. When the signed integer overflow occurs and produces a negative length value, the memory allocation functions may interpret this as a request for a large unsigned integer value, leading to unexpected memory layout changes or buffer overflows. This type of vulnerability falls under the CWE-190 category of "Integer Overflow or Wraparound" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: Unix Shell" when the vulnerability is exploited in shell contexts. The vulnerability is particularly dangerous because it can be triggered through normal string formatting operations, making it difficult to detect and prevent through standard input validation measures.
Mitigation strategies for CVE-2018-14337 require immediate attention from system administrators and developers using mruby 1.4.1. The primary recommendation involves upgrading to a patched version of mruby that addresses the integer overflow condition in the sprintf implementation. Organizations should also implement input validation measures that specifically check for negative length values before they reach the memory allocation functions. Additionally, deploying runtime protections such as address space layout randomization and stack canaries can help mitigate potential exploitation attempts. The vulnerability demonstrates the importance of proper integer handling in embedded systems and scripting engines, where seemingly benign operations can lead to critical security flaws. Security teams should monitor for exploitation attempts targeting this vulnerability and ensure that all affected systems are updated promptly to prevent potential compromise of applications relying on vulnerable mruby implementations.