jsonata CVE-2026-12208

Exploitation requires that the target application passes attacker-controlled or attacker-influenced content as keys within jsonata expressions or variable binding frames evaluated by createFrame in src/jsonata.js. Applications that evaluate only static, developer-authored jsonata expressions with no user-supplied key names are not directly exploitable. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N) confirms that no authentication, non-default configuration, or user interaction is required when attacker-controlled input reaches the vulnerable function - making this a zero-prerequisite network attack against any exposed jsonata evaluation endpoint. Exploitation is bounded by the application's data flow: the attacker must control or influence expression variable names or binding keys, not merely the data values being queried. The named hasOwnProperty bypass technique in the POC means that applications relying on the library's own guard - rather than external input sanitization - remain vulnerable even if they believe prototype-pollution defenses are present.

The CVSS 4.0 score of 6.9 (Medium) captures only the direct, base-level integrity impact (VI:L) and understates realistic risk. Prototype pollution vulnerabilities are structurally underscored by CVSS because downstream effects - authentication bypass, arbitrary code execution in chained logic, or denial of service in dependent code paths - are application-dependent and not reflected in base metrics. The zero-prerequisite CVSS profile (AV:N/AC:L/PR:N/UI:N) means any application endpoint that passes attacker-influenced data into jsonata expression evaluation is directly exploitable with no friction. The publicly available POC (E:P, GitHub: OriginSecurityX/jsonata-hasownproperty-bypass) significantly compresses the time-to-exploit and makes this accessible to non-specialist attackers. KEV status is not confirmed - CISA active exploitation is not established - so this should be characterized as opportunistic rather than confirmed targeted exploitation. EPSS data was not provided; however, the combination of zero-privilege network exploitability and a working public PoC warrants treating this as higher priority than the 6.9 base score suggests, particularly in applications that expose jsonata evaluation to untrusted input. The absence of any vendor patch response is the most significant risk multiplier: there is no timeline for remediation.

An attacker targeting a web application that evaluates user-supplied jsonata expressions sends a crafted query containing a payload that uses __proto__ or a similar prototype-chain key as a variable binding name within the expression, reaching the vulnerable createFrame function. Because the POC (https://github.com/OriginSecurityX/jsonata-hasownproperty-bypass) demonstrates a bypass of the hasOwnProperty guard, standard naive prototype-pollution defenses in the library are insufficient to block the injection. Once Object.prototype is polluted with attacker-chosen properties, downstream application logic that trusts inherited object properties - such as authorization checks, configuration lookups, or template rendering - may be subverted to escalate privileges, bypass authentication, or execute attacker-controlled code paths.