CVE-2026-82261 in SvelteKit
Summary
by MITRE • 08/28/2026
SvelteKit (@sveltejs/kit) versions >=2.49.0 and <=2.52.1 with experimental remote functions and form enabled contain a CPU exhaustion vulnerability in form deserialization. An attacker can send malformed form data to cause the server to become unresponsive while processing the request, resulting in denial of service. Fixed in 2.52.2.
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Analysis
by VulDB Data Team • 08/28/2026
The SvelteKit framework, specifically versions ranging from 2.49.0 through 2.52.1, contains a critical resource exhaustion vulnerability within its form deserialization logic when the experimental remote functions feature is enabled alongside standard form handling mechanisms. This flaw arises during the processing of incoming HTTP requests that contain multipart or URL-encoded form data intended for server-side function invocation. The underlying issue stems from an inefficient algorithmic complexity in how the framework parses and validates nested or deeply structured form payloads, leading to excessive CPU consumption rather than a memory leak or buffer overflow scenario. When an attacker submits specially crafted malformed form data characterized by deep nesting levels or repetitive complex structures, the deserialization engine enters a state of prolonged computation without proper bounds checking on recursion depth or iteration counts. This behavior allows a single request to monopolize server processing threads for an extended period, effectively blocking other legitimate requests from being processed and degrading overall system availability.
From a technical perspective, this vulnerability is classified under CWE-400, which denotes Uncontrolled Resource Consumption, specifically manifesting as CPU exhaustion or resource starvation. The attack vector leverages the application's trust in incoming form data structures to trigger computationally expensive operations during the serialization-to-deserialization pipeline. Because SvelteKit’s experimental remote functions allow client-side code to invoke server-side logic directly via HTTP calls that mimic standard form submissions, the framework must parse these payloads before routing them to the appropriate handler. The lack of safeguards against excessively complex or deeply nested data structures in this specific version range means that an unauthenticated attacker can exploit this flaw remotely over the network. This aligns with MITRE ATT&CK technique T1496, Resource Hijacking, where adversaries consume computational resources to disrupt service availability for other users. The impact is a classic denial of service condition, where the web server becomes unresponsive due to thread pool exhaustion or CPU saturation caused by the maliciously crafted requests.
The operational impact of this vulnerability extends beyond simple latency increases; it can lead to complete service outages if multiple concurrent attacks are launched against the affected endpoints. Since modern web servers often rely on limited worker threads, a few well-timed requests exploiting this deserialization flaw can saturate these resources, preventing legitimate traffic from being served. This results in HTTP 503 Service Unavailable errors for genuine users and potentially triggers automatic scaling events or crashes if the hosting environment has strict resource limits configured. The vulnerability is particularly dangerous because it does not require authentication, allowing any external actor to contribute to the denial of service condition. Furthermore, as this involves experimental features, administrators may have enabled them without fully understanding the associated security implications regarding input validation and resource management policies.
To mitigate this risk, organizations running SvelteKit versions within the affected range must immediately upgrade to version 2.52.2 or later, where the deserialization logic has been patched to include proper limits on recursion depth and payload complexity. Until an upgrade is feasible, administrators should consider disabling experimental remote functions if they are not strictly required for production workloads, thereby removing the attack surface entirely. Additionally implementing rate limiting at the network edge using a Web Application Firewall or reverse proxy can help mitigate the impact by throttling requests from single sources that exhibit patterns consistent with resource exhaustion attacks. Input validation strategies should also be reviewed to ensure that any custom form processing logic adheres to strict size and depth constraints, preventing overly complex structures from reaching the vulnerable deserialization code path. Regular security audits of framework dependencies are essential to identify such vulnerabilities in experimental features before they can be exploited in production environments.