CVE-2026-114142 in toml-node
Summary
by MITRE • 10/21/2026
toml-node is a TOML parser for Node.js and the browser. Prior to 5.0.1, toml.parse() can write attacker-controlled properties to Object.prototype because quoteDottedString() in lib/compiler.js produces the same bookkeeping string for distinct quoted key paths, allowing addTableArray() to clear another key's guard. The assign() path then descends through an unowned Date value without applying the owned-container check and can reach the prototype chain. Objects created elsewhere in the process can inherit the injected property. This issue is fixed in version 5.0.1.
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Analysis
by VulDB Data Team • 10/21/2026
The vulnerability identified in toml-node versions prior to 5.0.1 represents a critical Prototype Pollution flaw that stems from improper handling of object keys during the parsing of TOML formatted data. As a widely used library for parsing TOML configurations, any compromise in its integrity can lead to significant security implications across applications relying on it for configuration management or data serialization. The core technical issue resides within the lib/compiler.js module, specifically involving the quoteDottedString function and its interaction with addTableArray during the processing of parsed input.
The root cause lies in a collision of bookkeeping strings generated by quoteDottedString when processing distinct quoted key paths. In normal operation, these internal mechanisms are designed to track object ownership and prevent modifications to prototype chains or unowned containers that could lead to security bypasses. However, due to the aforementioned string collision, the library fails to correctly distinguish between different keys during the construction of nested objects. This confusion allows an attacker-controlled input to manipulate the internal state in a way that clears guards intended to protect specific key paths from unauthorized modification.
Once these protective mechanisms are neutralized through the addTableArray function, the assign path within the parser proceeds without applying necessary ownership checks on Date values or other container types. By descending into unowned containers and bypassing prototype chain protections, an attacker can inject properties directly onto Object.prototype. This is particularly dangerous because it affects all objects created subsequently in the same JavaScript execution context, regardless of their original intent or structure. The injection does not require complex exploitation techniques; simply providing a specifically crafted TOML string with maliciously formatted keys is sufficient to trigger the prototype pollution.
The operational impact of this vulnerability extends beyond simple data corruption. Prototype Pollution can lead to denial of service conditions if critical properties are overwritten, potentially crashing applications that depend on standard object methods or attributes. Furthermore, it opens the door for more severe attacks such as remote code execution in server-side environments where certain prototypes might be exploited to alter runtime behavior, bypass authentication checks by modifying prototype-based validation logic, or escalate privileges within the application context. Since JavaScript objects are dynamic and shared across many parts of an application, a single instance of polluted prototype can have widespread consequences throughout the entire system.
Mitigation strategies primarily involve upgrading to version 5.0.1 or later, where this specific flaw in key path handling has been resolved. For environments unable to immediately upgrade, implementing strict input validation on TOML data before parsing is recommended. Developers should also consider using Object.freeze() on configuration objects after initialization to prevent runtime modifications and avoid relying solely on library-level protections for security-critical operations. Additionally, employing sandboxing techniques or running untrusted code in isolated contexts can limit the blast radius of such vulnerabilities if they are encountered in legacy systems.
From a classification perspective, this vulnerability aligns with CWE-1325, which covers improper check for unusual input conditions leading to prototype pollution, and is closely related to CWE-915 regarding Improper Modification of Objects with Incorrectly Controlled Dynamically-Mapped References. In the context of the MITRE ATT&CK framework, this technique falls under Taint Analysis failures or potentially Command Injection if the polluted properties are used in subsequent dynamic evaluations, though it primarily represents a logic flaw in data processing rather than direct code execution. Understanding these mappings helps security teams prioritize remediation efforts and apply appropriate controls to prevent similar issues in other parsing libraries that may share analogous architectural patterns.