CVE-2019-19333 in libyang
Summary
by MITRE
In all versions of libyang before 1.0-r5, a stack-based buffer overflow was discovered in the way libyang parses YANG files with a leaf of type "bits". An application that uses libyang to parse untrusted YANG files may be vulnerable to this flaw, which would allow an attacker to cause a denial of service or possibly gain code execution.
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Analysis
by VulDB Data Team • 05/16/2025
The vulnerability identified as CVE-2019-19333 represents a critical stack-based buffer overflow in libyang versions prior to 1.0-r5, specifically affecting the parsing of YANG files containing leaf elements of type "bits". This flaw exists within the core parsing functionality of the libyang library, which serves as a crucial component for processing YANG data models in network configuration and management systems. The vulnerability stems from inadequate input validation during the parsing of structured data elements, creating a potential entry point for malicious actors to exploit the software's memory management mechanisms.
The technical implementation of this vulnerability occurs when libyang encounters YANG files containing leaf nodes with the "bits" data type, which is used to represent a set of named bits or flags within network configuration models. During parsing operations, the library fails to properly validate the size and structure of bit definitions, leading to a scenario where crafted input can exceed allocated stack buffer boundaries. This overflow condition can be triggered through specially constructed YANG files that manipulate the bit definition parameters, causing the program to write beyond its allocated memory space and potentially corrupt adjacent stack memory regions.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass potential code execution capabilities, making it particularly dangerous for systems that process untrusted YANG data. Applications utilizing libyang for configuration management, network device automation, or data model validation become vulnerable when processing external or user-provided YANG files without proper input sanitization. The vulnerability affects systems where libyang is embedded as a parsing library, including network operating systems, configuration management tools, and software-defined networking solutions that rely on YANG model validation for operational integrity.
Systems implementing mitigations for CVE-2019-19333 should prioritize updating to libyang version 1.0-r5 or later, which includes proper bounds checking and input validation for bit type parsing operations. Additionally, organizations should implement input validation policies that restrict the processing of untrusted YANG files, employ sandboxed parsing environments, and conduct regular security assessments of network configuration systems. The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory allocations, and represents a potential entry point for attackers following ATT&CK technique T1059.007 Command and Scripting Interpreter: Python, where malicious inputs could be crafted to exploit the buffer overflow for unauthorized code execution. Organizations should also consider implementing runtime protections such as stack canaries, address space layout randomization, and memory protection mechanisms to reduce the exploitability of similar vulnerabilities in their network infrastructure components.