CVE-2021-28903 in libyang
Summary
by MITRE • 05/21/2021
A stack overflow in libyang
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Analysis
by VulDB Data Team • 05/23/2021
The vulnerability identified as CVE-2021-28903 represents a critical stack overflow condition within the libyang library, a widely used YANG data modeling language parser and toolkit. This issue affects the parsing functionality of YANG data models, which are essential for configuring and managing network devices and applications that implement the Network Configuration Protocol. The stack overflow occurs when the library processes malformed or specially crafted YANG data structures, potentially leading to arbitrary code execution or system crashes. The vulnerability stems from insufficient input validation and boundary checking within the library's parsing routines, particularly when handling complex or nested data structures. This flaw exists in the core parsing logic that translates YANG schema definitions and data instances into internal representations for processing. The issue is particularly concerning because libyang is extensively integrated into network management systems, configuration tools, and software-defined networking solutions, making it a prime target for attackers seeking to compromise network infrastructure.
The technical implementation of this stack overflow involves improper handling of recursive data structures during the parsing phase of YANG documents. When the library encounters malformed input containing deeply nested elements or excessive recursion, the stack memory allocated for parsing operations becomes insufficient to accommodate the recursive calls. This results in memory corruption that can overwrite adjacent stack frames, potentially allowing attackers to manipulate program execution flow. The vulnerability manifests when the parser processes YANG data that contains excessive nesting levels or malformed schema constructs that trigger unbounded recursion. The flaw is categorized under CWE-121 Stack-based Buffer Overflow, which specifically addresses buffer overflows occurring in stack memory regions. The implementation does not properly validate the depth of recursive structures or enforce reasonable limits on parsing operations, creating an exploitable condition where attacker-controlled input can cause the stack to overflow.
The operational impact of this vulnerability extends across numerous network infrastructure components that rely on libyang for configuration management and data processing. Systems including network routers, switches, firewalls, and network management platforms that utilize this library for YANG data handling are at risk of being compromised. The vulnerability can be exploited remotely through configuration management interfaces, automated provisioning systems, or any network service that accepts YANG data inputs. Attackers can craft malicious YANG documents that trigger the stack overflow during processing, potentially leading to complete system compromise or denial of service conditions. The exploitation of this vulnerability aligns with ATT&CK technique T1210, which involves exploitation of remote services through manipulation of input data structures. Organizations using network devices, configuration management tools, or any system that parses YANG data are exposed to significant risk, particularly those implementing automated configuration deployment processes that may inadvertently process untrusted YANG inputs.
Mitigation strategies for CVE-2021-28903 require immediate patching of affected libyang versions, with priority given to systems handling untrusted YANG data inputs. Organizations should implement input validation measures that enforce reasonable limits on data structure nesting levels and recursion depth. Network segmentation and access controls should be strengthened to limit exposure of systems that process YANG data. Regular security assessments of network management systems and configuration tools that utilize libyang are essential to identify potential exploitation vectors. The implementation of monitoring systems to detect anomalous parsing behavior or unusual resource consumption patterns can help identify exploitation attempts. Additionally, organizations should consider implementing defensive programming practices such as stack canaries and address space layout randomization to mitigate potential exploitation. The vulnerability demonstrates the importance of robust input validation in parsing libraries and highlights the need for comprehensive security testing of data processing components. Regular updates to security patches and maintaining awareness of emerging threats in configuration management systems are crucial for preventing successful exploitation of similar vulnerabilities in the future.