CVE-2018-20993 in yaml-rust Crate
Summary
by MITRE
An issue was discovered in the yaml-rust crate before 0.4.1 for Rust. There is uncontrolled recursion during deserialization.
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Analysis
by VulDB Data Team • 12/04/2023
The yaml-rust crate vulnerability CVE-2018-20993 represents a critical security flaw that manifests during the deserialization process of yaml documents. This issue affects versions prior to 0.4.1 and stems from the crate's inability to properly handle recursive yaml structures during parsing operations. The vulnerability creates a condition where maliciously crafted yaml input can trigger infinite recursion, leading to potential system resource exhaustion and application instability. The flaw specifically impacts applications that rely on yaml-rust for processing untrusted yaml data, making it particularly dangerous in environments where input validation is insufficient.
The technical root cause of this vulnerability aligns with CWE-674, which describes uncontrolled recursion in software systems. During yaml deserialization, the parser fails to implement proper depth limits or recursion detection mechanisms when encountering nested structures within yaml documents. This allows attackers to craft yaml payloads containing deeply nested or cyclic references that cause the parser to recursively traverse the same structures indefinitely. The vulnerability operates at the parsing layer of the yaml-rust crate, where the deserialization logic lacks adequate safeguards against excessive nesting levels that could lead to stack overflow conditions or resource exhaustion attacks.
The operational impact of CVE-2018-20993 extends beyond simple denial of service scenarios, as it can be exploited to consume excessive system resources and potentially cause application crashes. Attackers can leverage this vulnerability by providing specially crafted yaml files that contain recursive references or deeply nested structures, causing the application to enter infinite loops during parsing. This creates a vector for resource exhaustion attacks where system memory and processing power are consumed rapidly, potentially leading to application instability or complete system failure. The vulnerability affects any application that processes external yaml input without proper validation or depth limiting measures, making it particularly concerning for web applications, configuration management systems, and any software that handles user-provided yaml data.
Mitigation strategies for CVE-2018-20993 should focus on immediate version upgrades to yaml-rust 0.4.1 or later, which includes proper recursion depth limiting mechanisms. Security practitioners should implement input validation and sanitization processes that restrict yaml document complexity before processing, particularly when handling untrusted input sources. Additionally, deploying runtime monitoring and resource limiting controls can help detect and prevent exploitation attempts by identifying abnormal resource consumption patterns. Organizations should also consider implementing application firewalls or web application firewalls that can detect and block suspicious yaml parsing patterns. The vulnerability demonstrates the importance of proper input validation and recursion control in parsing libraries, aligning with ATT&CK technique T1210 which covers exploitation of software vulnerabilities through resource exhaustion attacks. System administrators should conduct comprehensive vulnerability assessments to identify all applications using affected versions of yaml-rust and ensure proper patching across all environments.