CVE-2026-81176 in devalue
Summary
by MITRE • 09/16/2026
Svelte devalue is a JavaScript library that serializes values into strings when JSON.stringify isn't sufficient for the job. Prior to 5.9.2, devalue.parse does not reject out-of-bounds indices that are greater than or equal to values.length in src/parse.js. A specially crafted untrusted payload can make the parser alternate between array representations, producing quadratic work as the payload grows and causing denial of service in applications that parse untrusted devalue data. This issue is fixed in version 5.9.2.
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Analysis
by VulDB Data Team • 09/16/2026
The Svelte devalue library serves a specialized role in JavaScript ecosystems by providing serialization capabilities for values that standard JSON.stringify cannot handle, such as undefined, functions, or circular references. While this functionality offers significant utility for state management and data transfer within complex applications, it introduces specific security considerations when processing untrusted input. The core vulnerability identified involves the devalue.parse function, which is responsible for deserializing string representations back into JavaScript objects. Prior to version 5.9.2, the parser lacked adequate validation checks regarding array index boundaries during the parsing process. Specifically, the implementation failed to reject out-of-bounds indices that were greater than or equal to the current length of the target value array. This oversight allows an attacker to manipulate the internal state of the parser by providing crafted payloads containing invalid array references.
The technical flaw stems from a lack of bounds checking within the parsing logic in src/parse.js. When the parser encounters an index that exceeds the valid range for a given array, it does not immediately throw an error or halt execution as expected in secure implementations. Instead, this incorrect handling leads to erratic behavior where the parser alternates between different internal representations of arrays. This instability triggers a computational anomaly known as quadratic complexity growth relative to the size of the input payload. As the malicious data grows larger, the processing time increases exponentially rather than linearly. Consequently, an attacker can craft a relatively small but carefully structured string that forces the application's CPU to perform excessive calculations, effectively creating a Denial of Service condition. This type of vulnerability is classified under CWE-400, which covers Uncontrolled Resource Consumption, and aligns with ATT&CK technique T1496, representing Resource Hijacking where an attacker consumes resources to degrade service availability for legitimate users.
The operational impact of this vulnerability is primarily focused on application stability and resource exhaustion rather than data integrity or confidentiality breaches in the traditional sense. Applications that rely on Svelte devalue to parse user-supplied input are at risk if they do not implement additional safeguards such as rate limiting, request size limits, or timeout mechanisms. A successful exploitation could lead to server unresponsiveness, increased latency for all users, and potential crashes of long-running processes depending on the hosting environment's resource constraints. While this does not typically allow for remote code execution directly through the parser itself, it serves as a potent vector for disrupting service availability. The risk is heightened in scenarios where devalue parsing occurs synchronously or without adequate isolation from other critical application threads.
To mitigate this vulnerability, organizations must immediately upgrade to Svelte devalue version 5.9.2 or later, which includes the necessary bounds checking fixes. For applications that cannot update instantly due to dependency constraints, implementing input validation is crucial. This involves enforcing strict limits on the size of incoming payloads and rejecting any data that exceeds predefined thresholds before it reaches the parser. Additionally, integrating timeout mechanisms for parsing operations can prevent indefinite resource consumption. Security teams should also audit their use cases involving devalue to ensure that untrusted data is not being parsed directly without sanitization or validation layers in place. Regular security assessments focusing on serialization libraries are recommended to identify similar patterns of improper input handling across the technology stack.