CVE-2026-82258 in SvelteKit
Summary
by MITRE • 08/28/2026
SvelteKit versions from 2.38.0 before 2.60.1 contain a race condition in query.batch that allows concurrent requests from different users to merge under a single request context. Attackers can exploit specific timing conditions to access sensitive data from other users' concurrent requests.
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability identified in SvelteKit versions ranging from 2.38.0 up to, but not including, 2.60.1 represents a critical race condition within the query.batch functionality. This component is designed to optimize performance by grouping multiple data-fetching requests into a single network call or server-side execution context. However, due to improper handling of request contexts during concurrent operations, the framework fails to strictly isolate the state and session information associated with individual user sessions when batching queries. This architectural flaw allows an attacker who can trigger simultaneous requests from different users to exploit timing windows where these distinct contexts are incorrectly merged under a single processing scope.
From a technical perspective, the core issue lies in how SvelteKit manages asynchronous operations within its server-side rendering and API routing layers. When multiple clients send batched queries at nearly identical times, the internal event loop or middleware stack may reuse a shared context object intended for one user's request to process another user's data retrieval logic. This lack of strict isolation means that authentication tokens, session cookies, or other sensitive contextual metadata from User A can inadvertently be associated with the processing pipeline of User B. Consequently, when the server responds, it may return data fetched using User A's credentials but delivered in a response context where User B is authenticated, effectively bypassing access controls designed to restrict data visibility based on user identity.
The operational impact of this vulnerability is severe, primarily centering on unauthorized data disclosure and potential privilege escalation. An attacker can leverage specific timing conditions to force the server to merge requests from an unprivileged or different user with those of a privileged target. By carefully crafting concurrent requests, the adversary can cause the application to return sensitive information belonging to other users, such as personal identifiable information, financial records, or proprietary business data. This constitutes a direct violation of confidentiality principles and aligns closely with CWE-362, which describes Concurrent Execution using Shared Resource with Improper Synchronization leading to Race Conditions. Furthermore, because this involves accessing resources without proper authorization through the exploitation of timing flaws, it also maps to MITRE ATT&CK technique T1078, specifically within the context of Valid Accounts and Accessing Cloud Infrastructure or Internal Resources where identity is manipulated via race conditions.
Mitigation strategies for organizations utilizing affected versions must prioritize immediate software updates as the primary defense vector. Upgrading SvelteKit to version 2.60.1 or later resolves this issue by implementing stricter isolation mechanisms for request contexts within the query.batch system, ensuring that each concurrent operation maintains its own distinct session and authentication state regardless of timing overlaps. In scenarios where an upgrade is not immediately feasible due to dependency constraints or testing requirements, temporary mitigations should focus on reducing concurrency levels in high-traffic endpoints if possible, although this may impact performance. Additionally, implementing robust input validation and ensuring that all data-fetching operations explicitly verify the current user's identity against the requested resource before returning results can provide a secondary layer of defense. Security teams should also monitor logs for unusual patterns of concurrent requests from disparate IP addresses or sessions targeting sensitive endpoints, as these could indicate active exploitation attempts leveraging this race condition.