CVE-2018-7166 in Node.js
Summary
by MITRE
In all versions of Node.js 10 prior to 10.9.0, an argument processing flaw can cause `Buffer.alloc()` to return uninitialized memory. This method is intended to be safe and only return initialized, or cleared, memory. The third argument specifying `encoding` can be passed as a number, this is misinterpreted by `Buffer's` internal "fill" method as the `start` to a fill operation. This flaw may be abused where `Buffer.alloc()` arguments are derived from user input to return uncleared memory blocks that may contain sensitive information.
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Analysis
by VulDB Data Team • 05/04/2023
The vulnerability described in CVE-2018-7166 represents a critical flaw in Node.js version 10.x prior to 10.9.0 that fundamentally undermines the security assurances provided by the Buffer.alloc() method. This issue stems from improper argument handling within the Node.js runtime's memory allocation mechanisms, creating a scenario where developers expect safe memory initialization but instead receive uninitialized memory segments containing potentially sensitive data. The flaw specifically targets the third parameter of Buffer.alloc() which is intended to specify encoding but can be misinterpreted as a start position parameter due to flawed type checking logic.
The technical implementation of this vulnerability exploits a type confusion issue within Node.js's internal Buffer handling code. When Buffer.alloc() receives a numeric value as its third argument, the internal fill method incorrectly interprets this number as the starting position for a fill operation rather than as an encoding specification. This misinterpretation causes the allocation process to skip the proper initialization phase, resulting in memory blocks that retain their previous contents. The vulnerability falls under CWE-129, Input Validation and Representation, and CWE-125, Out-of-bounds Read, as it involves improper handling of input parameters that leads to memory exposure. The flaw is particularly dangerous because it can be triggered through user-controllable inputs, making it exploitable in scenarios where application developers rely on Buffer.alloc() for secure memory allocation.
The operational impact of this vulnerability extends beyond simple memory exposure, creating potential information disclosure risks that could compromise sensitive data. Attackers can craft inputs that cause Buffer.alloc() to return uninitialized memory containing remnants of previous operations, including passwords, cryptographic keys, or other confidential information stored in memory. This vulnerability aligns with ATT&CK technique T1005, Data from Local System, as it enables unauthorized access to memory contents that should remain protected. The flaw particularly affects applications that process user input through Buffer.alloc() calls, especially in web applications, APIs, or any system where user data flows into memory allocation functions. Systems handling sensitive information such as authentication tokens, personal data, or financial records are at heightened risk when running vulnerable Node.js versions.
Mitigation strategies for CVE-2018-7166 require immediate patching of affected Node.js installations to version 10.9.0 or later, which addresses the argument processing flaw through proper type validation and parameter handling. Organizations should implement comprehensive code reviews to identify all instances where Buffer.alloc() is used with potentially untrusted input, ensuring proper validation of parameters before memory allocation occurs. Security teams should also consider implementing runtime monitoring to detect unusual Buffer allocation patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and type safety in language runtimes, reinforcing principles from the OWASP Top 10 that emphasize the need for secure coding practices and proper memory management. Additionally, developers should avoid passing user-controllable data directly as arguments to memory allocation functions and implement proper sanitization or validation layers before such operations occur.