Recently, a significant security vulnerability, identified as CVE-2022-46175, was reported in the JSON5 library concerning prototype pollution. This issue was particularly noteworthy as it impacted the way the JSON5 parser handles certain special keys, such as __proto__. JSON5 is a more flexible iteration of JSON designed to be easier for humans to write and edit, and is mainly used in configuration files.
This vulnerability inside JSON5's parse method arises when parsing keys named __proto__. Under usual circumstances, this key should be ignored or treated specially to prevent potential security flaws. However, affected versions of JSON5 (up to 1.0.1 and 2.2.1) do not service this requirement, leading to the returned object's prototype getting polluted.
Prototype pollution can alter the expected behavior of software where the compromised object is reused. Depending on how the polluted object is utilized within applications, possible consequences include denial of service (DoS), unintended exposure of sensitive information, cross-site scripting (XSS), or elevation of privilege. In high-risk scenarios, it might even lead to remote code execution.
For developers and software maintainers, understanding and mitigating this issue is critical. The vulnerability has been resolved in the newer releases of JSON5 (versions 1.0.2, 2.2.2, and later). Upgrading to these secured versions is strongly recommended. Additionally, where upgrade is not immediately possible, considering alternatives such as using the default JSON.parse of JavaScript might offer temporary respite, as this function does not acknowledge __proto__ as anything other than a regular key.
Maintainers of software relying on JSON5 should perform a thorough audit of their applications' usage of the parsed data. It's essential to ensure that no critical operations depend on objects that are returned directly from parsing user input via JSON5. Proactively addressing these points will significantly diminish the risk associated with this vulnerability.
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