CVE-2018-20340 in libu2f-host
Summary
by MITRE
Yubico libu2f-host 1.1.6 contains unchecked buffers in devs.c, which could enable a malicious token to exploit a buffer overflow. An attacker could use this to attempt to execute malicious code using a crafted USB device masquerading as a security token on a computer where the affected library is currently in use. It is not possible to perform this attack with a genuine YubiKey.
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Analysis
by VulDB Data Team • 05/18/2020
The vulnerability identified as CVE-2018-20340 affects Yubico's libu2f-host library version 1.1.6, specifically within the devs.c source file where unchecked buffer operations exist. This flaw represents a classic buffer overflow vulnerability that occurs when the library fails to properly validate input lengths before copying data into fixed-size buffers. The affected library serves as a crucial component in USB security token communication, handling the low-level interactions between host systems and universal 2nd factor authentication devices. The vulnerability stems from inadequate bounds checking during device enumeration and data processing operations, creating opportunities for malicious actors to craft specially designed USB devices that can exploit these memory handling flaws.
The technical exploitation of this vulnerability requires an attacker to create a malicious USB device that can masquerade as a legitimate security token while simultaneously sending crafted data payloads that exceed the allocated buffer sizes. This type of attack falls under the CWE-121 CWE category for stack-based buffer overflow conditions, where insufficient bounds checking allows attackers to overwrite adjacent memory locations. The operational impact is significant as it could enable arbitrary code execution on systems where the vulnerable library is installed and actively processing USB device communications. Attackers could potentially leverage this vulnerability to escalate privileges, install malware, or perform other malicious activities that would otherwise be restricted by proper authentication mechanisms.
Security researchers have classified this vulnerability as particularly concerning due to its potential for remote exploitation through physical access vectors, where an attacker could simply connect a malicious USB device to a target system. The attack vector specifically targets the USB communication layer where legitimate security tokens interact with host systems, making it a critical concern for organizations that rely heavily on hardware security tokens for authentication and access control. This vulnerability operates at the intersection of physical security and software security, as it requires both the malicious hardware component and the vulnerable software stack to be present for successful exploitation. The attack model aligns with ATT&CK technique T1059.007 for command and scripting interpreter, where an attacker could potentially establish persistent access through code execution capabilities gained via buffer overflow exploitation.
Organizations should immediately update their libu2f-host library installations to versions that address the buffer overflow conditions in devs.c, typically through patch releases that implement proper bounds checking mechanisms. System administrators should conduct comprehensive inventory assessments to identify all systems running vulnerable versions of the library, particularly those in high-security environments where USB device access is permitted. Security teams should implement monitoring for suspicious USB device connections and establish procedures for device authentication verification. The mitigation strategy should include regular security updates, network segmentation to limit USB device access, and comprehensive vulnerability scanning to identify other potential buffer overflow conditions in similar libraries. Additionally, organizations should consider implementing USB device whitelisting policies and device authentication protocols to reduce the attack surface for such physical access-based exploits.