CVE-2026-82258 Overview
CVE-2026-82258 is a race condition vulnerability in SvelteKit affecting versions 2.38.0 through 2.60.0. The flaw resides in the query.batch function, where concurrent requests from different users can merge under a single request context. Attackers who trigger specific timing conditions can read sensitive data belonging to other users' concurrent requests. The vulnerability is classified under [CWE-362] (Concurrent Execution using Shared Resource with Improper Synchronization).
Critical Impact
Concurrent requests from different users can share a request context in SvelteKit query.batch, exposing sensitive per-user data to unrelated sessions under timing-dependent conditions.
Affected Products
- SvelteKit 2.38.0 through 2.60.0 (Node.js runtime)
- Applications using query.batch for server-side data fetching
- Any downstream project pinning a vulnerable SvelteKit release
Discovery Timeline
- 2026-08-28 - CVE-2026-82258 published to NVD
- 2026-08-31 - Last updated in NVD database
Technical Details for CVE-2026-82258
Vulnerability Analysis
SvelteKit exposes a query.batch mechanism that groups multiple data queries into a single server-side execution to reduce round trips. In affected versions, the batching layer reuses a request context across concurrent inbound requests when timing conditions align. Two users hitting the same batching path in overlapping windows can end up sharing state such as authenticated user identity, cookies, or query results. This produces cross-user data disclosure without any authentication bypass on the attacker's part.
The issue is a classic concurrency defect: request-scoped data is placed in a location that is not strictly isolated per request. When the runtime interleaves execution across asynchronous boundaries, the second request may observe or receive results computed against the first request's identity.
Root Cause
The root cause is improper synchronization of per-request state inside query.batch. The batching path treats context as effectively shared during the batch window instead of binding it to a single request's async scope. Under sufficient concurrency, contexts merge and outputs cross request boundaries.
Attack Vector
Exploitation requires network access to a SvelteKit application that uses query.batch on routes returning user-specific data. An attacker must issue requests timed to overlap with a victim's session activity, which is why the attack complexity is high and user interaction is required. Successful exploitation returns data intended for a different user in the attacker's response. See the GitHub Security Advisory GHSA-hgv7-v322-mmgr and the VulnCheck advisory for technical details.
Detection Methods for CVE-2026-82258
Indicators of Compromise
- Application logs showing responses containing user identifiers or records that do not match the authenticated session on the request.
- Anomalous correlation between concurrent request bursts and user-reported data leakage on routes using query.batch.
- Support tickets reporting that users saw another account's data after a page load or navigation.
Detection Strategies
- Inventory SvelteKit dependencies via package-lock.json or pnpm-lock.yaml and flag any @sveltejs/kit version between 2.38.0 and 2.60.0.
- Add integration tests that fire overlapping authenticated requests against query.batch endpoints and assert per-user response isolation.
- Instrument server-side handlers to log the resolved user ID alongside outgoing response payload identifiers for post-hoc mismatch analysis.
Monitoring Recommendations
- Alert on spikes in concurrent requests to routes backed by query.batch from distinct sessions targeting the same handler.
- Track error rates and content-length anomalies on batched endpoints as a proxy for context merging.
- Retain application access logs long enough to correlate cross-user disclosure reports with request timing windows.
How to Mitigate CVE-2026-82258
Immediate Actions Required
- Upgrade @sveltejs/kit to version 2.60.1 or later across all environments.
- Audit routes that use query.batch for handling of authenticated or otherwise sensitive per-user data.
- Rotate session tokens if evidence suggests cross-user disclosure occurred in production traffic.
Patch Information
The fix is available in SvelteKit 2.60.1. Refer to the GitHub Security Advisory GHSA-hgv7-v322-mmgr for the upstream advisory and remediation guidance.
Workarounds
- Avoid query.batch on routes that return user-scoped data until the upgrade is deployed.
- Refactor sensitive handlers to fetch data individually rather than through the batching API.
- Enforce per-request context propagation explicitly using async-local storage patterns in server code that must remain on affected versions.
# Upgrade SvelteKit to a fixed release
npm install @sveltejs/kit@^2.60.1
# Verify the resolved version
npm ls @sveltejs/kit
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
