CVE-2018-16396 in Ruby
Summary
by MITRE
An issue was discovered in Ruby before 2.3.8, 2.4.x before 2.4.5, 2.5.x before 2.5.2, and 2.6.x before 2.6.0-preview3. It does not taint strings that result from unpacking tainted strings with some formats.
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Analysis
by VulDB Data Team • 06/06/2023
This vulnerability resides in the ruby programming language's handling of tainted string data, specifically within the unpacking functionality of the core library. The issue affects multiple ruby version streams including 2.3.x through 2.3.7, 2.4.x through 2.4.4, 2.5.x through 2.5.1, and 2.6.x prior to the preview3 release. The flaw represents a critical breakdown in ruby's security model where the taint propagation mechanism fails to properly handle strings that are the result of unpacking tainted data using certain format specifiers.
The technical root cause involves ruby's taint checking system which is designed to track potentially unsafe data that originates from external sources such as user input, file reads, or network communications. When ruby processes data through its unpack method with specific format strings, the system should maintain the taint status of the resulting strings to prevent potential security issues. However, this vulnerability allows certain unpack operations to produce untainted strings even when they are derived from tainted source data, effectively bypassing ruby's built-in security safeguards.
The operational impact of this vulnerability is significant within applications that rely on ruby's taint checking for security purposes. Attackers could exploit this weakness by crafting malicious input that, when unpacked through vulnerable ruby versions, produces untainted strings that would otherwise be flagged as potentially dangerous. This creates opportunities for bypassing security controls that depend on taint tracking, potentially enabling code execution attacks, data leakage, or other malicious activities that rely on manipulating tainted data flows.
This vulnerability maps to CWE-1232 which specifically addresses the improper handling of taint information in programming languages, and aligns with ATT&CK technique T1059.007 for executing malicious code through scripting languages. The flaw particularly impacts applications that use ruby's taint checking as part of their security architecture, including web applications, security tools, and systems that process untrusted data through ruby-based processing pipelines. Organizations running ruby applications on affected versions face increased risk of security bypasses that could compromise their applications and underlying systems.
The recommended mitigation strategy involves upgrading to ruby versions that have patched this vulnerability, specifically ruby 2.3.8, 2.4.5, 2.5.2, or 2.6.0-preview3 and later releases. Additionally, administrators should implement proper input validation and sanitization measures as defense-in-depth controls, even when running patched versions. Applications should avoid relying solely on ruby's taint checking for security decisions and instead implement comprehensive security controls that verify data integrity and source authenticity through multiple validation layers.