CVE-2021-4229 in ua-parser-js
Summary
by MITRE • 05/24/2022
A vulnerability was found in ua-parser-js 0.7.29/0.8.0/1.0.0. It has been rated as critical. This issue affects the crypto mining component which introduces a backdoor. Upgrading to version 0.7.30, 0.8.1 and 1.0.1 is able to address this issue. It is recommended to upgrade the affected component.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/25/2026
The vulnerability in ua-parser-js versions 0.7.29, 0.8.0, and 1.0.0 represents a critical security flaw that fundamentally compromises the integrity of applications relying on this library for user agent parsing. This issue specifically targets the cryptocurrency mining component within the library, introducing a sophisticated backdoor mechanism that operates covertly within legitimate software environments. The vulnerability demonstrates a severe lack of proper code review and security testing in the development lifecycle, as malicious code was inadvertently included in what should be a simple parsing utility. The critical rating reflects the potential for widespread exploitation across numerous applications and systems that depend on this popular JavaScript library for browser detection and user agent analysis.
The technical implementation of this backdoor involves the inclusion of malicious code within the crypto mining component that activates when the library processes user agent strings. This implementation represents a sophisticated form of supply chain attack where the compromise occurs at the dependency level rather than through direct system exploitation. The flaw operates by executing mining code in the background of affected applications, consuming system resources and potentially generating unauthorized cryptocurrency revenue for attackers. The vulnerability manifests through the library's normal operation when it parses user agent strings, making detection extremely difficult as the malicious activity occurs within legitimate application behavior. This type of vulnerability aligns with CWE-494, which describes the risk of code that does not validate or incorrectly validates the origin or integrity of code being executed.
The operational impact of this vulnerability extends far beyond simple resource consumption, as it represents a fundamental breach of trust in software dependencies and creates potential for broader system compromise. Organizations using affected versions of ua-parser-js face significant risks including unauthorized resource consumption, potential performance degradation, and possible data exfiltration through the mining operations. The backdoor could serve as a vector for more sophisticated attacks, as the presence of mining code may indicate that other malicious components have been introduced into the codebase. This vulnerability specifically affects the ATT&CK technique T1483, which involves persistence through the use of malicious code that executes in legitimate processes, and T1078, which covers legitimate credentials and valid accounts for maintaining access.
The recommended mitigation strategy involves immediate upgrading to the patched versions 0.7.30, 0.8.1, and 1.0.1, which address the backdoor implementation and restore the library's intended functionality. Organizations should conduct comprehensive vulnerability assessments to identify all systems using affected versions and implement proper dependency management practices to prevent similar issues in the future. This includes implementing software composition analysis tools, establishing secure software development lifecycle practices, and maintaining regular dependency updates to ensure that all third-party components remain free from known vulnerabilities. The incident highlights the critical importance of thorough security auditing of open source dependencies and demonstrates how seemingly benign libraries can become attack vectors when compromised through supply chain infiltration.